Fixed MTP to work with TWRP

Documentation/accounting/Makefile

@@ -0,0 +1,7 @@
+# List of programs to build
+hostprogs-y := getdelays
+
+# Tell kbuild to always build the programs
+always := $(hostprogs-y)
+
+HOSTCFLAGS_getdelays.o += -I$(objtree)/usr/include

Documentation/accounting/cgroupstats.txt

@@ -0,0 +1,27 @@
+Control Groupstats is inspired by the discussion at
+http://lkml.org/lkml/2007/4/11/187 and implements per cgroup statistics as
+suggested by Andrew Morton in http://lkml.org/lkml/2007/4/11/263.
+
+Per cgroup statistics infrastructure re-uses code from the taskstats
+interface. A new set of cgroup operations are registered with commands
+and attributes specific to cgroups. It should be very easy to
+extend per cgroup statistics, by adding members to the cgroupstats
+structure.
+
+The current model for cgroupstats is a pull, a push model (to post
+statistics on interesting events), should be very easy to add. Currently
+user space requests for statistics by passing the cgroup path.
+Statistics about the state of all the tasks in the cgroup is returned to
+user space.
+
+NOTE: We currently rely on delay accounting for extracting information
+about tasks blocked on I/O. If CONFIG_TASK_DELAY_ACCT is disabled, this
+information will not be available.
+
+To extract cgroup statistics a utility very similar to getdelays.c
+has been developed, the sample output of the utility is shown below
+
+~/balbir/cgroupstats # ./getdelays  -C "/sys/fs/cgroup/a"
+sleeping 1, blocked 0, running 1, stopped 0, uninterruptible 0
+~/balbir/cgroupstats # ./getdelays  -C "/sys/fs/cgroup"
+sleeping 155, blocked 0, running 1, stopped 0, uninterruptible 2

Documentation/accounting/delay-accounting.txt

@@ -0,0 +1,117 @@
+Delay accounting
+----------------
+
+Tasks encounter delays in execution when they wait
+for some kernel resource to become available e.g. a
+runnable task may wait for a free CPU to run on.
+
+The per-task delay accounting functionality measures
+the delays experienced by a task while
+
+a) waiting for a CPU (while being runnable)
+b) completion of synchronous block I/O initiated by the task
+c) swapping in pages
+d) memory reclaim
+
+and makes these statistics available to userspace through
+the taskstats interface.
+
+Such delays provide feedback for setting a task's cpu priority,
+io priority and rss limit values appropriately. Long delays for
+important tasks could be a trigger for raising its corresponding priority.
+
+The functionality, through its use of the taskstats interface, also provides
+delay statistics aggregated for all tasks (or threads) belonging to a
+thread group (corresponding to a traditional Unix process). This is a commonly
+needed aggregation that is more efficiently done by the kernel.
+
+Userspace utilities, particularly resource management applications, can also
+aggregate delay statistics into arbitrary groups. To enable this, delay
+statistics of a task are available both during its lifetime as well as on its
+exit, ensuring continuous and complete monitoring can be done.
+
+
+Interface
+---------
+
+Delay accounting uses the taskstats interface which is described
+in detail in a separate document in this directory. Taskstats returns a
+generic data structure to userspace corresponding to per-pid and per-tgid
+statistics. The delay accounting functionality populates specific fields of
+this structure. See
+     include/linux/taskstats.h
+for a description of the fields pertaining to delay accounting.
+It will generally be in the form of counters returning the cumulative
+delay seen for cpu, sync block I/O, swapin, memory reclaim etc.
+
+Taking the difference of two successive readings of a given
+counter (say cpu_delay_total) for a task will give the delay
+experienced by the task waiting for the corresponding resource
+in that interval.
+
+When a task exits, records containing the per-task statistics
+are sent to userspace without requiring a command. If it is the last exiting
+task of a thread group, the per-tgid statistics are also sent. More details
+are given in the taskstats interface description.
+
+The getdelays.c userspace utility in this directory allows simple commands to
+be run and the corresponding delay statistics to be displayed. It also serves
+as an example of using the taskstats interface.
+
+Usage
+-----
+
+Compile the kernel with
+	CONFIG_TASK_DELAY_ACCT=y
+	CONFIG_TASKSTATS=y
+
+Delay accounting is enabled by default at boot up.
+To disable, add
+   nodelayacct
+to the kernel boot options. The rest of the instructions
+below assume this has not been done.
+
+After the system has booted up, use a utility
+similar to  getdelays.c to access the delays
+seen by a given task or a task group (tgid).
+The utility also allows a given command to be
+executed and the corresponding delays to be
+seen.
+
+General format of the getdelays command
+
+getdelays [-t tgid] [-p pid] [-c cmd...]
+
+
+Get delays, since system boot, for pid 10
+# ./getdelays -p 10
+(output similar to next case)
+
+Get sum of delays, since system boot, for all pids with tgid 5
+# ./getdelays -t 5
+
+
+CPU	count	real total	virtual total	delay total
+	7876	92005750	100000000	24001500
+IO	count	delay total
+	0	0
+SWAP	count	delay total
+	0	0
+RECLAIM	count	delay total
+	0	0
+
+Get delays seen in executing a given simple command
+# ./getdelays -c ls /
+
+bin   data1  data3  data5  dev  home  media  opt   root  srv        sys  usr
+boot  data2  data4  data6  etc  lib   mnt    proc  sbin  subdomain  tmp  var
+
+
+CPU	count	real total	virtual total	delay total
+	6	4000250		4000000		0
+IO	count	delay total
+	0	0
+SWAP	count	delay total
+	0	0
+RECLAIM	count	delay total
+	0	0

Documentation/accounting/getdelays.c

@@ -0,0 +1,546 @@
+/* getdelays.c
+ *
+ * Utility to get per-pid and per-tgid delay accounting statistics
+ * Also illustrates usage of the taskstats interface
+ *
+ * Copyright (C) Shailabh Nagar, IBM Corp. 2005
+ * Copyright (C) Balbir Singh, IBM Corp. 2006
+ * Copyright (c) Jay Lan, SGI. 2006
+ *
+ * Compile with
+ *	gcc -I/usr/src/linux/include getdelays.c -o getdelays
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <unistd.h>
+#include <poll.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+#include <linux/genetlink.h>
+#include <linux/taskstats.h>
+#include <linux/cgroupstats.h>
+
+/*
+ * Generic macros for dealing with netlink sockets. Might be duplicated
+ * elsewhere. It is recommended that commercial grade applications use
+ * libnl or libnetlink and use the interfaces provided by the library
+ */
+#define GENLMSG_DATA(glh)	((void *)(NLMSG_DATA(glh) + GENL_HDRLEN))
+#define GENLMSG_PAYLOAD(glh)	(NLMSG_PAYLOAD(glh, 0) - GENL_HDRLEN)
+#define NLA_DATA(na)		((void *)((char*)(na) + NLA_HDRLEN))
+#define NLA_PAYLOAD(len)	(len - NLA_HDRLEN)
+
+#define err(code, fmt, arg...)			\
+	do {					\
+		fprintf(stderr, fmt, ##arg);	\
+		exit(code);			\
+	} while (0)
+
+int done;
+int rcvbufsz;
+char name[100];
+int dbg;
+int print_delays;
+int print_io_accounting;
+int print_task_context_switch_counts;
+
+#define PRINTF(fmt, arg...) {			\
+	    if (dbg) {				\
+		printf(fmt, ##arg);		\
+	    }					\
+	}
+
+/* Maximum size of response requested or message sent */
+#define MAX_MSG_SIZE	1024
+/* Maximum number of cpus expected to be specified in a cpumask */
+#define MAX_CPUS	32
+
+struct msgtemplate {
+	struct nlmsghdr n;
+	struct genlmsghdr g;
+	char buf[MAX_MSG_SIZE];
+};
+
+char cpumask[100+6*MAX_CPUS];
+
+static void usage(void)
+{
+	fprintf(stderr, "getdelays [-dilv] [-w logfile] [-r bufsize] "
+			"[-m cpumask] [-t tgid] [-p pid]\n");
+	fprintf(stderr, "  -d: print delayacct stats\n");
+	fprintf(stderr, "  -i: print IO accounting (works only with -p)\n");
+	fprintf(stderr, "  -l: listen forever\n");
+	fprintf(stderr, "  -v: debug on\n");
+	fprintf(stderr, "  -C: container path\n");
+}
+
+/*
+ * Create a raw netlink socket and bind
+ */
+static int create_nl_socket(int protocol)
+{
+	int fd;
+	struct sockaddr_nl local;
+
+	fd = socket(AF_NETLINK, SOCK_RAW, protocol);
+	if (fd < 0)
+		return -1;
+
+	if (rcvbufsz)
+		if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF,
+				&rcvbufsz, sizeof(rcvbufsz)) < 0) {
+			fprintf(stderr, "Unable to set socket rcv buf size to %d\n",
+				rcvbufsz);
+			goto error;
+		}
+
+	memset(&local, 0, sizeof(local));
+	local.nl_family = AF_NETLINK;
+
+	if (bind(fd, (struct sockaddr *) &local, sizeof(local)) < 0)
+		goto error;
+
+	return fd;
+error:
+	close(fd);
+	return -1;
+}
+
+
+static int send_cmd(int sd, __u16 nlmsg_type, __u32 nlmsg_pid,
+	     __u8 genl_cmd, __u16 nla_type,
+	     void *nla_data, int nla_len)
+{
+	struct nlattr *na;
+	struct sockaddr_nl nladdr;
+	int r, buflen;
+	char *buf;
+
+	struct msgtemplate msg;
+
+	msg.n.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
+	msg.n.nlmsg_type = nlmsg_type;
+	msg.n.nlmsg_flags = NLM_F_REQUEST;
+	msg.n.nlmsg_seq = 0;
+	msg.n.nlmsg_pid = nlmsg_pid;
+	msg.g.cmd = genl_cmd;
+	msg.g.version = 0x1;
+	na = (struct nlattr *) GENLMSG_DATA(&msg);
+	na->nla_type = nla_type;
+	na->nla_len = nla_len + 1 + NLA_HDRLEN;
+	memcpy(NLA_DATA(na), nla_data, nla_len);
+	msg.n.nlmsg_len += NLMSG_ALIGN(na->nla_len);
+
+	buf = (char *) &msg;
+	buflen = msg.n.nlmsg_len ;
+	memset(&nladdr, 0, sizeof(nladdr));
+	nladdr.nl_family = AF_NETLINK;
+	while ((r = sendto(sd, buf, buflen, 0, (struct sockaddr *) &nladdr,
+			   sizeof(nladdr))) < buflen) {
+		if (r > 0) {
+			buf += r;
+			buflen -= r;
+		} else if (errno != EAGAIN)
+			return -1;
+	}
+	return 0;
+}
+
+
+/*
+ * Probe the controller in genetlink to find the family id
+ * for the TASKSTATS family
+ */
+static int get_family_id(int sd)
+{
+	struct {
+		struct nlmsghdr n;
+		struct genlmsghdr g;
+		char buf[256];
+	} ans;
+
+	int id = 0, rc;
+	struct nlattr *na;
+	int rep_len;
+
+	strcpy(name, TASKSTATS_GENL_NAME);
+	rc = send_cmd(sd, GENL_ID_CTRL, getpid(), CTRL_CMD_GETFAMILY,
+			CTRL_ATTR_FAMILY_NAME, (void *)name,
+			strlen(TASKSTATS_GENL_NAME)+1);
+	if (rc < 0)
+		return 0;	/* sendto() failure? */
+
+	rep_len = recv(sd, &ans, sizeof(ans), 0);
+	if (ans.n.nlmsg_type == NLMSG_ERROR ||
+	    (rep_len < 0) || !NLMSG_OK((&ans.n), rep_len))
+		return 0;
+
+	na = (struct nlattr *) GENLMSG_DATA(&ans);
+	na = (struct nlattr *) ((char *) na + NLA_ALIGN(na->nla_len));
+	if (na->nla_type == CTRL_ATTR_FAMILY_ID) {
+		id = *(__u16 *) NLA_DATA(na);
+	}
+	return id;
+}
+
+#define average_ms(t, c) (t / 1000000ULL / (c ? c : 1))
+
+static void print_delayacct(struct taskstats *t)
+{
+	printf("\n\nCPU   %15s%15s%15s%15s%15s\n"
+	       "      %15llu%15llu%15llu%15llu%15.3fms\n"
+	       "IO    %15s%15s%15s\n"
+	       "      %15llu%15llu%15llums\n"
+	       "SWAP  %15s%15s%15s\n"
+	       "      %15llu%15llu%15llums\n"
+	       "RECLAIM  %12s%15s%15s\n"
+	       "      %15llu%15llu%15llums\n",
+	       "count", "real total", "virtual total",
+	       "delay total", "delay average",
+	       (unsigned long long)t->cpu_count,
+	       (unsigned long long)t->cpu_run_real_total,
+	       (unsigned long long)t->cpu_run_virtual_total,
+	       (unsigned long long)t->cpu_delay_total,
+	       average_ms((double)t->cpu_delay_total, t->cpu_count),
+	       "count", "delay total", "delay average",
+	       (unsigned long long)t->blkio_count,
+	       (unsigned long long)t->blkio_delay_total,
+	       average_ms(t->blkio_delay_total, t->blkio_count),
+	       "count", "delay total", "delay average",
+	       (unsigned long long)t->swapin_count,
+	       (unsigned long long)t->swapin_delay_total,
+	       average_ms(t->swapin_delay_total, t->swapin_count),
+	       "count", "delay total", "delay average",
+	       (unsigned long long)t->freepages_count,
+	       (unsigned long long)t->freepages_delay_total,
+	       average_ms(t->freepages_delay_total, t->freepages_count));
+}
+
+static void task_context_switch_counts(struct taskstats *t)
+{
+	printf("\n\nTask   %15s%15s\n"
+	       "       %15llu%15llu\n",
+	       "voluntary", "nonvoluntary",
+	       (unsigned long long)t->nvcsw, (unsigned long long)t->nivcsw);
+}
+
+static void print_cgroupstats(struct cgroupstats *c)
+{
+	printf("sleeping %llu, blocked %llu, running %llu, stopped %llu, "
+		"uninterruptible %llu\n", (unsigned long long)c->nr_sleeping,
+		(unsigned long long)c->nr_io_wait,
+		(unsigned long long)c->nr_running,
+		(unsigned long long)c->nr_stopped,
+		(unsigned long long)c->nr_uninterruptible);
+}
+
+
+static void print_ioacct(struct taskstats *t)
+{
+	printf("%s: read=%llu, write=%llu, cancelled_write=%llu\n",
+		t->ac_comm,
+		(unsigned long long)t->read_bytes,
+		(unsigned long long)t->write_bytes,
+		(unsigned long long)t->cancelled_write_bytes);
+}
+
+int main(int argc, char *argv[])
+{
+	int c, rc, rep_len, aggr_len, len2;
+	int cmd_type = TASKSTATS_CMD_ATTR_UNSPEC;
+	__u16 id;
+	__u32 mypid;
+
+	struct nlattr *na;
+	int nl_sd = -1;
+	int len = 0;
+	pid_t tid = 0;
+	pid_t rtid = 0;
+
+	int fd = 0;
+	int count = 0;
+	int write_file = 0;
+	int maskset = 0;
+	char *logfile = NULL;
+	int loop = 0;
+	int containerset = 0;
+	char *containerpath = NULL;
+	int cfd = 0;
+	int forking = 0;
+	sigset_t sigset;
+
+	struct msgtemplate msg;
+
+	while (!forking) {
+		c = getopt(argc, argv, "qdiw:r:m:t:p:vlC:c:");
+		if (c < 0)
+			break;
+
+		switch (c) {
+		case 'd':
+			printf("print delayacct stats ON\n");
+			print_delays = 1;
+			break;
+		case 'i':
+			printf("printing IO accounting\n");
+			print_io_accounting = 1;
+			break;
+		case 'q':
+			printf("printing task/process context switch rates\n");
+			print_task_context_switch_counts = 1;
+			break;
+		case 'C':
+			containerset = 1;
+			containerpath = optarg;
+			break;
+		case 'w':
+			logfile = strdup(optarg);
+			printf("write to file %s\n", logfile);
+			write_file = 1;
+			break;
+		case 'r':
+			rcvbufsz = atoi(optarg);
+			printf("receive buf size %d\n", rcvbufsz);
+			if (rcvbufsz < 0)
+				err(1, "Invalid rcv buf size\n");
+			break;
+		case 'm':
+			strncpy(cpumask, optarg, sizeof(cpumask));
+			cpumask[sizeof(cpumask) - 1] = '\0';
+			maskset = 1;
+			printf("cpumask %s maskset %d\n", cpumask, maskset);
+			break;
+		case 't':
+			tid = atoi(optarg);
+			if (!tid)
+				err(1, "Invalid tgid\n");
+			cmd_type = TASKSTATS_CMD_ATTR_TGID;
+			break;
+		case 'p':
+			tid = atoi(optarg);
+			if (!tid)
+				err(1, "Invalid pid\n");
+			cmd_type = TASKSTATS_CMD_ATTR_PID;
+			break;
+		case 'c':
+
+			/* Block SIGCHLD for sigwait() later */
+			if (sigemptyset(&sigset) == -1)
+				err(1, "Failed to empty sigset");
+			if (sigaddset(&sigset, SIGCHLD))
+				err(1, "Failed to set sigchld in sigset");
+			sigprocmask(SIG_BLOCK, &sigset, NULL);
+
+			/* fork/exec a child */
+			tid = fork();
+			if (tid < 0)
+				err(1, "Fork failed\n");
+			if (tid == 0)
+				if (execvp(argv[optind - 1],
+				    &argv[optind - 1]) < 0)
+					exit(-1);
+
+			/* Set the command type and avoid further processing */
+			cmd_type = TASKSTATS_CMD_ATTR_PID;
+			forking = 1;
+			break;
+		case 'v':
+			printf("debug on\n");
+			dbg = 1;
+			break;
+		case 'l':
+			printf("listen forever\n");
+			loop = 1;
+			break;
+		default:
+			usage();
+			exit(-1);
+		}
+	}
+
+	if (write_file) {
+		fd = open(logfile, O_WRONLY | O_CREAT | O_TRUNC,
+			  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+		if (fd == -1) {
+			perror("Cannot open output file\n");
+			exit(1);
+		}
+	}
+
+	if ((nl_sd = create_nl_socket(NETLINK_GENERIC)) < 0)
+		err(1, "error creating Netlink socket\n");
+
+
+	mypid = getpid();
+	id = get_family_id(nl_sd);
+	if (!id) {
+		fprintf(stderr, "Error getting family id, errno %d\n", errno);
+		goto err;
+	}
+	PRINTF("family id %d\n", id);
+
+	if (maskset) {
+		rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
+			      TASKSTATS_CMD_ATTR_REGISTER_CPUMASK,
+			      &cpumask, strlen(cpumask) + 1);
+		PRINTF("Sent register cpumask, retval %d\n", rc);
+		if (rc < 0) {
+			fprintf(stderr, "error sending register cpumask\n");
+			goto err;
+		}
+	}
+
+	if (tid && containerset) {
+		fprintf(stderr, "Select either -t or -C, not both\n");
+		goto err;
+	}
+
+	/*
+	 * If we forked a child, wait for it to exit. Cannot use waitpid()
+	 * as all the delicious data would be reaped as part of the wait
+	 */
+	if (tid && forking) {
+		int sig_received;
+		sigwait(&sigset, &sig_received);
+	}
+
+	if (tid) {
+		rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
+			      cmd_type, &tid, sizeof(__u32));
+		PRINTF("Sent pid/tgid, retval %d\n", rc);
+		if (rc < 0) {
+			fprintf(stderr, "error sending tid/tgid cmd\n");
+			goto done;
+		}
+	}
+
+	if (containerset) {
+		cfd = open(containerpath, O_RDONLY);
+		if (cfd < 0) {
+			perror("error opening container file");
+			goto err;
+		}
+		rc = send_cmd(nl_sd, id, mypid, CGROUPSTATS_CMD_GET,
+			      CGROUPSTATS_CMD_ATTR_FD, &cfd, sizeof(__u32));
+		if (rc < 0) {
+			perror("error sending cgroupstats command");
+			goto err;
+		}
+	}
+	if (!maskset && !tid && !containerset) {
+		usage();
+		goto err;
+	}
+
+	do {
+		rep_len = recv(nl_sd, &msg, sizeof(msg), 0);
+		PRINTF("received %d bytes\n", rep_len);
+
+		if (rep_len < 0) {
+			fprintf(stderr, "nonfatal reply error: errno %d\n",
+				errno);
+			continue;
+		}
+		if (msg.n.nlmsg_type == NLMSG_ERROR ||
+		    !NLMSG_OK((&msg.n), rep_len)) {
+			struct nlmsgerr *err = NLMSG_DATA(&msg);
+			fprintf(stderr, "fatal reply error,  errno %d\n",
+				err->error);
+			goto done;
+		}
+
+		PRINTF("nlmsghdr size=%zu, nlmsg_len=%d, rep_len=%d\n",
+		       sizeof(struct nlmsghdr), msg.n.nlmsg_len, rep_len);
+
+
+		rep_len = GENLMSG_PAYLOAD(&msg.n);
+
+		na = (struct nlattr *) GENLMSG_DATA(&msg);
+		len = 0;
+		while (len < rep_len) {
+			len += NLA_ALIGN(na->nla_len);
+			switch (na->nla_type) {
+			case TASKSTATS_TYPE_AGGR_TGID:
+				/* Fall through */
+			case TASKSTATS_TYPE_AGGR_PID:
+				aggr_len = NLA_PAYLOAD(na->nla_len);
+				len2 = 0;
+				/* For nested attributes, na follows */
+				na = (struct nlattr *) NLA_DATA(na);
+				done = 0;
+				while (len2 < aggr_len) {
+					switch (na->nla_type) {
+					case TASKSTATS_TYPE_PID:
+						rtid = *(int *) NLA_DATA(na);
+						if (print_delays)
+							printf("PID\t%d\n", rtid);
+						break;
+					case TASKSTATS_TYPE_TGID:
+						rtid = *(int *) NLA_DATA(na);
+						if (print_delays)
+							printf("TGID\t%d\n", rtid);
+						break;
+					case TASKSTATS_TYPE_STATS:
+						count++;
+						if (print_delays)
+							print_delayacct((struct taskstats *) NLA_DATA(na));
+						if (print_io_accounting)
+							print_ioacct((struct taskstats *) NLA_DATA(na));
+						if (print_task_context_switch_counts)
+							task_context_switch_counts((struct taskstats *) NLA_DATA(na));
+						if (fd) {
+							if (write(fd, NLA_DATA(na), na->nla_len) < 0) {
+								err(1,"write error\n");
+							}
+						}
+						if (!loop)
+							goto done;
+						break;
+					default:
+						fprintf(stderr, "Unknown nested"
+							" nla_type %d\n",
+							na->nla_type);
+						break;
+					}
+					len2 += NLA_ALIGN(na->nla_len);
+					na = (struct nlattr *) ((char *) na + len2);
+				}
+				break;
+
+			case CGROUPSTATS_TYPE_CGROUP_STATS:
+				print_cgroupstats(NLA_DATA(na));
+				break;
+			default:
+				fprintf(stderr, "Unknown nla_type %d\n",
+					na->nla_type);
+			case TASKSTATS_TYPE_NULL:
+				break;
+			}
+			na = (struct nlattr *) (GENLMSG_DATA(&msg) + len);
+		}
+	} while (loop);
+done:
+	if (maskset) {
+		rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
+			      TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK,
+			      &cpumask, strlen(cpumask) + 1);
+		printf("Sent deregister mask, retval %d\n", rc);
+		if (rc < 0)
+			err(rc, "error sending deregister cpumask\n");
+	}
+err:
+	close(nl_sd);
+	if (fd)
+		close(fd);
+	if (cfd)
+		close(cfd);
+	return 0;
+}

Documentation/accounting/taskstats-struct.txt

@@ -0,0 +1,180 @@
+The struct taskstats
+--------------------
+
+This document contains an explanation of the struct taskstats fields.
+
+There are three different groups of fields in the struct taskstats:
+
+1) Common and basic accounting fields
+    If CONFIG_TASKSTATS is set, the taskstats interface is enabled and
+    the common fields and basic accounting fields are collected for
+    delivery at do_exit() of a task.
+2) Delay accounting fields
+    These fields are placed between
+    /* Delay accounting fields start */
+    and
+    /* Delay accounting fields end */
+    Their values are collected if CONFIG_TASK_DELAY_ACCT is set.
+3) Extended accounting fields
+    These fields are placed between
+    /* Extended accounting fields start */
+    and
+    /* Extended accounting fields end */
+    Their values are collected if CONFIG_TASK_XACCT is set.
+
+4) Per-task and per-thread context switch count statistics
+
+5) Time accounting for SMT machines
+
+6) Extended delay accounting fields for memory reclaim
+
+Future extension should add fields to the end of the taskstats struct, and
+should not change the relative position of each field within the struct.
+
+
+struct taskstats {
+
+1) Common and basic accounting fields:
+	/* The version number of this struct. This field is always set to
+	 * TAKSTATS_VERSION, which is defined in <linux/taskstats.h>.
+	 * Each time the struct is changed, the value should be incremented.
+	 */
+	__u16	version;
+
+  	/* The exit code of a task. */
+	__u32	ac_exitcode;		/* Exit status */
+
+  	/* The accounting flags of a task as defined in <linux/acct.h>
+	 * Defined values are AFORK, ASU, ACOMPAT, ACORE, and AXSIG.
+	 */
+	__u8	ac_flag;		/* Record flags */
+
+  	/* The value of task_nice() of a task. */
+	__u8	ac_nice;		/* task_nice */
+
+  	/* The name of the command that started this task. */
+	char	ac_comm[TS_COMM_LEN];	/* Command name */
+
+  	/* The scheduling discipline as set in task->policy field. */
+	__u8	ac_sched;		/* Scheduling discipline */
+
+	__u8	ac_pad[3];
+	__u32	ac_uid;			/* User ID */
+	__u32	ac_gid;			/* Group ID */
+	__u32	ac_pid;			/* Process ID */
+	__u32	ac_ppid;		/* Parent process ID */
+
+  	/* The time when a task begins, in [secs] since 1970. */
+	__u32	ac_btime;		/* Begin time [sec since 1970] */
+
+  	/* The elapsed time of a task, in [usec]. */
+	__u64	ac_etime;		/* Elapsed time [usec] */
+
+  	/* The user CPU time of a task, in [usec]. */
+	__u64	ac_utime;		/* User CPU time [usec] */
+
+  	/* The system CPU time of a task, in [usec]. */
+	__u64	ac_stime;		/* System CPU time [usec] */
+
+  	/* The minor page fault count of a task, as set in task->min_flt. */
+	__u64	ac_minflt;		/* Minor Page Fault Count */
+
+	/* The major page fault count of a task, as set in task->maj_flt. */
+	__u64	ac_majflt;		/* Major Page Fault Count */
+
+
+2) Delay accounting fields:
+	/* Delay accounting fields start
+	 *
+	 * All values, until the comment "Delay accounting fields end" are
+	 * available only if delay accounting is enabled, even though the last
+	 * few fields are not delays
+	 *
+	 * xxx_count is the number of delay values recorded
+	 * xxx_delay_total is the corresponding cumulative delay in nanoseconds
+	 *
+	 * xxx_delay_total wraps around to zero on overflow
+	 * xxx_count incremented regardless of overflow
+	 */
+
+	/* Delay waiting for cpu, while runnable
+	 * count, delay_total NOT updated atomically
+	 */
+	__u64	cpu_count;
+	__u64	cpu_delay_total;
+
+	/* Following four fields atomically updated using task->delays->lock */
+
+	/* Delay waiting for synchronous block I/O to complete
+	 * does not account for delays in I/O submission
+	 */
+	__u64	blkio_count;
+	__u64	blkio_delay_total;
+
+	/* Delay waiting for page fault I/O (swap in only) */
+	__u64	swapin_count;
+	__u64	swapin_delay_total;
+
+	/* cpu "wall-clock" running time
+	 * On some architectures, value will adjust for cpu time stolen
+	 * from the kernel in involuntary waits due to virtualization.
+	 * Value is cumulative, in nanoseconds, without a corresponding count
+	 * and wraps around to zero silently on overflow
+	 */
+	__u64	cpu_run_real_total;
+
+	/* cpu "virtual" running time
+	 * Uses time intervals seen by the kernel i.e. no adjustment
+	 * for kernel's involuntary waits due to virtualization.
+	 * Value is cumulative, in nanoseconds, without a corresponding count
+	 * and wraps around to zero silently on overflow
+	 */
+	__u64	cpu_run_virtual_total;
+	/* Delay accounting fields end */
+	/* version 1 ends here */
+
+
+3) Extended accounting fields
+	/* Extended accounting fields start */
+
+	/* Accumulated RSS usage in duration of a task, in MBytes-usecs.
+	 * The current rss usage is added to this counter every time
+	 * a tick is charged to a task's system time. So, at the end we
+	 * will have memory usage multiplied by system time. Thus an
+	 * average usage per system time unit can be calculated.
+	 */
+	__u64	coremem;		/* accumulated RSS usage in MB-usec */
+
+  	/* Accumulated virtual memory usage in duration of a task.
+	 * Same as acct_rss_mem1 above except that we keep track of VM usage.
+	 */
+	__u64	virtmem;		/* accumulated VM usage in MB-usec */
+
+  	/* High watermark of RSS usage in duration of a task, in KBytes. */
+	__u64	hiwater_rss;		/* High-watermark of RSS usage */
+
+  	/* High watermark of VM  usage in duration of a task, in KBytes. */
+	__u64	hiwater_vm;		/* High-water virtual memory usage */
+
+	/* The following four fields are I/O statistics of a task. */
+	__u64	read_char;		/* bytes read */
+	__u64	write_char;		/* bytes written */
+	__u64	read_syscalls;		/* read syscalls */
+	__u64	write_syscalls;		/* write syscalls */
+
+	/* Extended accounting fields end */
+
+4) Per-task and per-thread statistics
+	__u64	nvcsw;			/* Context voluntary switch counter */
+	__u64	nivcsw;			/* Context involuntary switch counter */
+
+5) Time accounting for SMT machines
+	__u64	ac_utimescaled;		/* utime scaled on frequency etc */
+	__u64	ac_stimescaled;		/* stime scaled on frequency etc */
+	__u64	cpu_scaled_run_real_total; /* scaled cpu_run_real_total */
+
+6) Extended delay accounting fields for memory reclaim
+	/* Delay waiting for memory reclaim */
+	__u64	freepages_count;
+	__u64	freepages_delay_total;
+}

Documentation/accounting/taskstats.txt

@@ -0,0 +1,181 @@
+Per-task statistics interface
+-----------------------------
+
+
+Taskstats is a netlink-based interface for sending per-task and
+per-process statistics from the kernel to userspace.
+
+Taskstats was designed for the following benefits:
+
+- efficiently provide statistics during lifetime of a task and on its exit
+- unified interface for multiple accounting subsystems
+- extensibility for use by future accounting patches
+
+Terminology
+-----------
+
+"pid", "tid" and "task" are used interchangeably and refer to the standard
+Linux task defined by struct task_struct.  per-pid stats are the same as
+per-task stats.
+
+"tgid", "process" and "thread group" are used interchangeably and refer to the
+tasks that share an mm_struct i.e. the traditional Unix process. Despite the
+use of tgid, there is no special treatment for the task that is thread group
+leader - a process is deemed alive as long as it has any task belonging to it.
+
+Usage
+-----
+
+To get statistics during a task's lifetime, userspace opens a unicast netlink
+socket (NETLINK_GENERIC family) and sends commands specifying a pid or a tgid.
+The response contains statistics for a task (if pid is specified) or the sum of
+statistics for all tasks of the process (if tgid is specified).
+
+To obtain statistics for tasks which are exiting, the userspace listener
+sends a register command and specifies a cpumask. Whenever a task exits on
+one of the cpus in the cpumask, its per-pid statistics are sent to the
+registered listener. Using cpumasks allows the data received by one listener
+to be limited and assists in flow control over the netlink interface and is
+explained in more detail below.
+
+If the exiting task is the last thread exiting its thread group,
+an additional record containing the per-tgid stats is also sent to userspace.
+The latter contains the sum of per-pid stats for all threads in the thread
+group, both past and present.
+
+getdelays.c is a simple utility demonstrating usage of the taskstats interface
+for reporting delay accounting statistics. Users can register cpumasks,
+send commands and process responses, listen for per-tid/tgid exit data,
+write the data received to a file and do basic flow control by increasing
+receive buffer sizes.
+
+Interface
+---------
+
+The user-kernel interface is encapsulated in include/linux/taskstats.h
+
+To avoid this documentation becoming obsolete as the interface evolves, only
+an outline of the current version is given. taskstats.h always overrides the
+description here.
+
+struct taskstats is the common accounting structure for both per-pid and
+per-tgid data. It is versioned and can be extended by each accounting subsystem
+that is added to the kernel. The fields and their semantics are defined in the
+taskstats.h file.
+
+The data exchanged between user and kernel space is a netlink message belonging
+to the NETLINK_GENERIC family and using the netlink attributes interface.
+The messages are in the format
+
+    +----------+- - -+-------------+-------------------+
+    | nlmsghdr | Pad |  genlmsghdr | taskstats payload |
+    +----------+- - -+-------------+-------------------+
+
+
+The taskstats payload is one of the following three kinds:
+
+1. Commands: Sent from user to kernel. Commands to get data on
+a pid/tgid consist of one attribute, of type TASKSTATS_CMD_ATTR_PID/TGID,
+containing a u32 pid or tgid in the attribute payload. The pid/tgid denotes
+the task/process for which userspace wants statistics.
+
+Commands to register/deregister interest in exit data from a set of cpus
+consist of one attribute, of type
+TASKSTATS_CMD_ATTR_REGISTER/DEREGISTER_CPUMASK and contain a cpumask in the
+attribute payload. The cpumask is specified as an ascii string of
+comma-separated cpu ranges e.g. to listen to exit data from cpus 1,2,3,5,7,8
+the cpumask would be "1-3,5,7-8". If userspace forgets to deregister interest
+in cpus before closing the listening socket, the kernel cleans up its interest
+set over time. However, for the sake of efficiency, an explicit deregistration
+is advisable.
+
+2. Response for a command: sent from the kernel in response to a userspace
+command. The payload is a series of three attributes of type:
+
+a) TASKSTATS_TYPE_AGGR_PID/TGID : attribute containing no payload but indicates
+a pid/tgid will be followed by some stats.
+
+b) TASKSTATS_TYPE_PID/TGID: attribute whose payload is the pid/tgid whose stats
+are being returned.
+
+c) TASKSTATS_TYPE_STATS: attribute with a struct taskstats as payload. The
+same structure is used for both per-pid and per-tgid stats.
+
+3. New message sent by kernel whenever a task exits. The payload consists of a
+   series of attributes of the following type:
+
+a) TASKSTATS_TYPE_AGGR_PID: indicates next two attributes will be pid+stats
+b) TASKSTATS_TYPE_PID: contains exiting task's pid
+c) TASKSTATS_TYPE_STATS: contains the exiting task's per-pid stats
+d) TASKSTATS_TYPE_AGGR_TGID: indicates next two attributes will be tgid+stats
+e) TASKSTATS_TYPE_TGID: contains tgid of process to which task belongs
+f) TASKSTATS_TYPE_STATS: contains the per-tgid stats for exiting task's process
+
+
+per-tgid stats
+--------------
+
+Taskstats provides per-process stats, in addition to per-task stats, since
+resource management is often done at a process granularity and aggregating task
+stats in userspace alone is inefficient and potentially inaccurate (due to lack
+of atomicity).
+
+However, maintaining per-process, in addition to per-task stats, within the
+kernel has space and time overheads. To address this, the taskstats code
+accumulates each exiting task's statistics into a process-wide data structure.
+When the last task of a process exits, the process level data accumulated also
+gets sent to userspace (along with the per-task data).
+
+When a user queries to get per-tgid data, the sum of all other live threads in
+the group is added up and added to the accumulated total for previously exited
+threads of the same thread group.
+
+Extending taskstats
+-------------------
+
+There are two ways to extend the taskstats interface to export more
+per-task/process stats as patches to collect them get added to the kernel
+in future:
+
+1. Adding more fields to the end of the existing struct taskstats. Backward
+   compatibility is ensured by the version number within the
+   structure. Userspace will use only the fields of the struct that correspond
+   to the version its using.
+
+2. Defining separate statistic structs and using the netlink attributes
+   interface to return them. Since userspace processes each netlink attribute
+   independently, it can always ignore attributes whose type it does not
+   understand (because it is using an older version of the interface).
+
+
+Choosing between 1. and 2. is a matter of trading off flexibility and
+overhead. If only a few fields need to be added, then 1. is the preferable
+path since the kernel and userspace don't need to incur the overhead of
+processing new netlink attributes. But if the new fields expand the existing
+struct too much, requiring disparate userspace accounting utilities to
+unnecessarily receive large structures whose fields are of no interest, then
+extending the attributes structure would be worthwhile.
+
+Flow control for taskstats
+--------------------------
+
+When the rate of task exits becomes large, a listener may not be able to keep
+up with the kernel's rate of sending per-tid/tgid exit data leading to data
+loss. This possibility gets compounded when the taskstats structure gets
+extended and the number of cpus grows large.
+
+To avoid losing statistics, userspace should do one or more of the following:
+
+- increase the receive buffer sizes for the netlink sockets opened by
+listeners to receive exit data.
+
+- create more listeners and reduce the number of cpus being listened to by
+each listener. In the extreme case, there could be one listener for each cpu.
+Users may also consider setting the cpu affinity of the listener to the subset
+of cpus to which it listens, especially if they are listening to just one cpu.
+
+Despite these measures, if the userspace receives ENOBUFS error messages
+indicated overflow of receive buffers, it should take measures to handle the
+loss of data.
+
+----