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Subject[Patch 7/8] documentation

delayacct-doc.patch

Some documentation for delay accounting.

Signed-off-by: Shailabh Nagar <nagar@watson.ibm.com>
Signed-off-by: Balbir Singh <balbir@in.ibm.com>
---
Documentation/accounting/delay-accounting.txt | 115 +++++++
Documentation/accounting/getdelays.c | 376 ++++++++++++++++++++++++++
Documentation/accounting/taskstats.txt | 2
3 files changed, 493 insertions(+)
diff -puN /dev/null Documentation/accounting/delay-accounting.txt
--- /dev/null 2004-06-24 23:34:38.000000000 +0530
+++ linux-2.6.17-rc3-balbir/Documentation/accounting/delay-accounting.txt 2006-05-02 10:36:37.000000000 +0530
@@ -0,0 +1,115 @@
+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
+
+
+
+
+
+
diff -puN /dev/null Documentation/accounting/getdelays.c
--- /dev/null 2004-06-24 23:34:38.000000000 +0530
+++ linux-2.6.17-rc3-balbir/Documentation/accounting/getdelays.c 2006-05-02 10:36:37.000000000 +0530
@@ -0,0 +1,376 @@
+/* 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;
+}
diff -puN Documentation/accounting/taskstats.txt~delayacct-doc Documentation/accounting/taskstats.txt
--- linux-2.6.17-rc3/Documentation/accounting/taskstats.txt~delayacct-doc 2006-05-02 10:36:37.000000000 +0530
+++ linux-2.6.17-rc3-balbir/Documentation/accounting/taskstats.txt 2006-05-02 10:36:37.000000000 +0530
@@ -39,6 +39,8 @@ belongs (the task does not need to be th
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
---------
_
-
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