[PATCH] per-task-delay-accounting: documentation

Some documentation for delay accounting.
Signed-off-by: Shailabh Nagar <nagar@watson.ibm.com>
Signed-off-by: Balbir Singh <balbir@in.ibm.com>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Peter Chubb <peterc@gelato.unsw.edu.au>
Cc: Erich Focht <efocht@ess.nec.de>
Cc: Levent Serinol <lserinol@gmail.com>
Cc: Jay Lan <jlan@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/accounting/delay-accounting.txt

+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
+
+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 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 and per-process statistics
+are sent to userspace without requiring a command. 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
+
+Enable the accounting at boot time by adding
+the following to the kernel boot options
+	delayacct
+
+and 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
+MEM	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
+MEM	count	delay total
+	0	0
+
+
+
+
+
+

Documentation/accounting/getdelays.c

+/* 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
+ *
+ */
+
+#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/types.h>
+#include <signal.h>
+
+#include <linux/genetlink.h>
+#include <linux/taskstats.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 { printf(fmt, ##arg); exit(code); } while (0)
+int done = 0;
+
+/*
+ * Create a raw netlink socket and bind
+ */
+static int create_nl_socket(int protocol, int groups)
+{
+    socklen_t addr_len;
+    int fd;
+    struct sockaddr_nl local;
+
+    fd = socket(AF_NETLINK, SOCK_RAW, protocol);
+    if (fd < 0)
+	return -1;
+
+    memset(&local, 0, sizeof(local));
+    local.nl_family = AF_NETLINK;
+    local.nl_groups = groups;
+
+    if (bind(fd, (struct sockaddr *) &local, sizeof(local)) < 0)
+	goto error;
+
+    return fd;
+  error:
+    close(fd);
+    return -1;
+}
+
+int sendto_fd(int s, const char *buf, int bufLen)
+{
+    struct sockaddr_nl nladdr;
+    int r;
+
+    memset(&nladdr, 0, sizeof(nladdr));
+    nladdr.nl_family = AF_NETLINK;
+
+    while ((r = sendto(s, 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
+ */
+int get_family_id(int sd)
+{
+    struct {
+	struct nlmsghdr n;
+	struct genlmsghdr g;
+	char buf[256];
+    } family_req;
+    struct {
+	struct nlmsghdr n;
+	struct genlmsghdr g;
+	char buf[256];
+    } ans;
+
+    int id;
+    struct nlattr *na;
+    int rep_len;
+
+    /* Get family name */
+    family_req.n.nlmsg_type = GENL_ID_CTRL;
+    family_req.n.nlmsg_flags = NLM_F_REQUEST;
+    family_req.n.nlmsg_seq = 0;
+    family_req.n.nlmsg_pid = getpid();
+    family_req.n.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
+    family_req.g.cmd = CTRL_CMD_GETFAMILY;
+    family_req.g.version = 0x1;
+    na = (struct nlattr *) GENLMSG_DATA(&family_req);
+    na->nla_type = CTRL_ATTR_FAMILY_NAME;
+    na->nla_len = strlen(TASKSTATS_GENL_NAME) + 1 + NLA_HDRLEN;
+    strcpy(NLA_DATA(na), TASKSTATS_GENL_NAME);
+    family_req.n.nlmsg_len += NLMSG_ALIGN(na->nla_len);
+
+    if (sendto_fd(sd, (char *) &family_req, family_req.n.nlmsg_len) < 0)
+	err(1, "error sending message via Netlink\n");
+
+    rep_len = recv(sd, &ans, sizeof(ans), 0);
+
+    if (rep_len < 0)
+	err(1, "error receiving reply message via Netlink\n");
+
+
+    /* Validate response message */
+    if (!NLMSG_OK((&ans.n), rep_len))
+	err(1, "invalid reply message received via Netlink\n");
+
+    if (ans.n.nlmsg_type == NLMSG_ERROR) {	/* error */
+	printf("error received NACK - leaving\n");
+	exit(1);
+    }
+
+
+    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;
+}
+
+void print_taskstats(struct taskstats *t)
+{
+    printf("\n\nCPU   %15s%15s%15s%15s\n"
+	   "      %15llu%15llu%15llu%15llu\n"
+	   "IO    %15s%15s\n"
+	   "      %15llu%15llu\n"
+	   "MEM   %15s%15s\n"
+	   "      %15llu%15llu\n\n",
+	   "count", "real total", "virtual total", "delay total",
+	   t->cpu_count, t->cpu_run_real_total, t->cpu_run_virtual_total,
+	   t->cpu_delay_total,
+	   "count", "delay total",
+	   t->blkio_count, t->blkio_delay_total,
+	   "count", "delay total", t->swapin_count, t->swapin_delay_total);
+}
+
+void sigchld(int sig)
+{
+    done = 1;
+}
+
+int main(int argc, char *argv[])
+{
+    int rc;
+    int sk_nl;
+    struct nlmsghdr *nlh;
+    struct genlmsghdr *genlhdr;
+    char *buf;
+    struct taskstats_cmd_param *param;
+    __u16 id;
+    struct nlattr *na;
+
+    /* For receiving */
+    struct sockaddr_nl kern_nla, from_nla;
+    socklen_t from_nla_len;
+    int recv_len;
+    struct taskstats_reply *reply;
+
+    struct {
+	struct nlmsghdr n;
+	struct genlmsghdr g;
+	char buf[256];
+    } req;
+
+    struct {
+	struct nlmsghdr n;
+	struct genlmsghdr g;
+	char buf[256];
+    } ans;
+
+    int nl_sd = -1;
+    int rep_len;
+    int len = 0;
+    int aggr_len, len2;
+    struct sockaddr_nl nladdr;
+    pid_t tid = 0;
+    pid_t rtid = 0;
+    int cmd_type = TASKSTATS_TYPE_TGID;
+    int c, status;
+    int forking = 0;
+    struct sigaction act = {
+	.sa_handler = SIG_IGN,
+	.sa_mask = SA_NOMASK,
+    };
+    struct sigaction tact ;
+
+    if (argc < 3) {
+	printf("usage %s [-t tgid][-p pid][-c cmd]\n", argv[0]);
+	exit(-1);
+    }
+
+    tact.sa_handler = sigchld;
+    sigemptyset(&tact.sa_mask);
+    if (sigaction(SIGCHLD, &tact, NULL) < 0)
+	err(1, "sigaction failed for SIGCHLD\n");
+
+    while (1) {
+
+	c = getopt(argc, argv, "t:p:c:");
+	if (c < 0)
+	    break;
+
+	switch (c) {
+	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_TGID;
+	    break;
+	case 'c':
+	    opterr = 0;
+	    tid = fork();
+	    if (tid < 0)
+		err(1, "fork failed\n");
+
+	    if (tid == 0) {	/* child process */
+		if (execvp(argv[optind - 1], &argv[optind - 1]) < 0) {
+		    exit(-1);
+		}
+	    }
+	    forking = 1;
+	    break;
+	default:
+	    printf("usage %s [-t tgid][-p pid][-c cmd]\n", argv[0]);
+	    exit(-1);
+	    break;
+	}
+	if (c == 'c')
+	    break;
+    }
+
+    /* Construct Netlink request message */
+
+    /* Send Netlink request message & get reply */
+
+    if ((nl_sd =
+	 create_nl_socket(NETLINK_GENERIC, TASKSTATS_LISTEN_GROUP)) < 0)
+	err(1, "error creating Netlink socket\n");
+
+
+    id = get_family_id(nl_sd);
+
+    /* Send command needed */
+    req.n.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
+    req.n.nlmsg_type = id;
+    req.n.nlmsg_flags = NLM_F_REQUEST;
+    req.n.nlmsg_seq = 0;
+    req.n.nlmsg_pid = tid;
+    req.g.cmd = TASKSTATS_CMD_GET;
+    na = (struct nlattr *) GENLMSG_DATA(&req);
+    na->nla_type = cmd_type;
+    na->nla_len = sizeof(unsigned int) + NLA_HDRLEN;
+    *(__u32 *) NLA_DATA(na) = tid;
+    req.n.nlmsg_len += NLMSG_ALIGN(na->nla_len);
+
+
+    if (!forking && sendto_fd(nl_sd, (char *) &req, req.n.nlmsg_len) < 0)
+	err(1, "error sending message via Netlink\n");
+
+    act.sa_handler = SIG_IGN;
+    sigemptyset(&act.sa_mask);
+    if (sigaction(SIGINT, &act, NULL) < 0)
+	err(1, "sigaction failed for SIGINT\n");
+
+    do {
+	int i;
+	struct pollfd pfd;
+	int pollres;
+
+	pfd.events = 0xffff & ~POLLOUT;
+	pfd.fd = nl_sd;
+	pollres = poll(&pfd, 1, 5000);
+	if (pollres < 0 || done) {
+	    break;
+	}
+
+	rep_len = recv(nl_sd, &ans, sizeof(ans), 0);
+	nladdr.nl_family = AF_NETLINK;
+	nladdr.nl_groups = TASKSTATS_LISTEN_GROUP;
+
+	if (ans.n.nlmsg_type == NLMSG_ERROR) {	/* error */
+	    printf("error received NACK - leaving\n");
+	    exit(1);
+	}
+
+	if (rep_len < 0) {
+	    err(1, "error receiving reply message via Netlink\n");
+	    break;
+	}
+
+	/* Validate response message */
+	if (!NLMSG_OK((&ans.n), rep_len))
+	    err(1, "invalid reply message received via Netlink\n");
+
+	rep_len = GENLMSG_PAYLOAD(&ans.n);
+
+	na = (struct nlattr *) GENLMSG_DATA(&ans);
+	len = 0;
+	i = 0;
+	while (len < rep_len) {
+	    len += NLA_ALIGN(na->nla_len);
+	    switch (na->nla_type) {
+	    case TASKSTATS_TYPE_AGGR_PID:
+		/* Fall through */
+	    case TASKSTATS_TYPE_AGGR_TGID:
+		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);
+			break;
+		    case TASKSTATS_TYPE_TGID:
+			rtid = *(int *) NLA_DATA(na);
+			break;
+		    case TASKSTATS_TYPE_STATS:
+			if (rtid == tid) {
+			    print_taskstats((struct taskstats *)
+					    NLA_DATA(na));
+			    done = 1;
+			}
+			break;
+		    }
+		    len2 += NLA_ALIGN(na->nla_len);
+		    na = (struct nlattr *) ((char *) na + len2);
+		    if (done)
+			break;
+		}
+	    }
+	    na = (struct nlattr *) (GENLMSG_DATA(&ans) + len);
+	    if (done)
+		break;
+	}
+	if (done)
+	    break;
+    }
+    while (1);
+
+    close(nl_sd);
+    return 0;
+}

Documentation/accounting/taskstats.txt

@@ -39,6 +39,8 @@ belongs (the task does not need to be the thread group leader). The need for
 per-tgid stats to be sent for each exiting task is explained in the per-tgid
 stats section below.
 
+getdelays.c is a simple utility demonstrating usage of the taskstats interface
+for reporting delay accounting statistics.
 
 Interface
 ---------