[PATCH] per task delay accounting taskstats interface: documentation fix

Change documentation and example program to reflect the flow control issues
being addressed by the cpumask changes.

Signed-off-by: Shailabh Nagar <nagar@watson.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/Documentation/accounting/getdelays.c b/Documentation/accounting/getdelays.c
index 33de89e56a3d38993fc12aab0a9f79b00b469fc0..795ca3911cc58f7fd043a6e51b95df8e9bff449f 100644 (file)
--- a/Documentation/accounting/getdelays.c
+++ b/Documentation/accounting/getdelays.c
@@ -5,6 +5,7 @@
  *
  * Copyright (C) Shailabh Nagar, IBM Corp. 2005
  * Copyright (C) Balbir Singh, IBM Corp. 2006
  *
  * Copyright (C) Shailabh Nagar, IBM Corp. 2005
  * Copyright (C) Balbir Singh, IBM Corp. 2006

+ * Copyright (c) Jay Lan, SGI. 2006

  *
  */
 
  *
  */
 


@@ -36,341 +37,360 @@
 
 #define err(code, fmt, arg...) do { printf(fmt, ##arg); exit(code); } while (0)
 int done = 0;
 
 #define err(code, fmt, arg...) do { printf(fmt, ##arg); exit(code); } while (0)
 int done = 0;

+int rcvbufsz=0;
+
+    char name[100];
+int dbg=0, print_delays=0;
+__u64 stime, utime;
+#define PRINTF(fmt, arg...) {                  \
+           if (dbg) {                          \
+               printf(fmt, ##arg);             \
+           }                                   \
+       }
+
+/* Maximum size of response requested or message sent */
+#define MAX_MSG_SIZE   256
+/* Maximum number of cpus expected to be specified in a cpumask */
+#define MAX_CPUS       32
+/* Maximum length of pathname to log file */
+#define MAX_FILENAME   256
+
+struct msgtemplate {
+       struct nlmsghdr n;
+       struct genlmsghdr g;
+       char buf[MAX_MSG_SIZE];
+};
+
+char cpumask[100+6*MAX_CPUS];

 
 /*
  * Create a raw netlink socket and bind
  */
 
 /*
  * Create a raw netlink socket and bind
  */

-static int create_nl_socket(int protocol, int groups)
+static int create_nl_socket(int protocol)

 {
 {

-    socklen_t addr_len;
-    int fd;
-    struct sockaddr_nl local;
-
-    fd = socket(AF_NETLINK, SOCK_RAW, protocol);
-    if (fd < 0)
-       return -1;
+       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) {
+                       printf("Unable to set socket rcv buf size to %d\n",
+                              rcvbufsz);
+                       return -1;
+               }

 
 

-    memset(&local, 0, sizeof(local));
-    local.nl_family = AF_NETLINK;
-    local.nl_groups = groups;
+       memset(&local, 0, sizeof(local));
+       local.nl_family = AF_NETLINK;

 
 

-    if (bind(fd, (struct sockaddr *) &local, sizeof(local)) < 0)
-       goto error;
+       if (bind(fd, (struct sockaddr *) &local, sizeof(local)) < 0)
+               goto error;

 
 

-    return fd;
-  error:
-    close(fd);
-    return -1;
+       return fd;
+error:
+       close(fd);
+       return -1;

 }
 
 }
 

-int sendto_fd(int s, const char *buf, int bufLen)
+
+int send_cmd(int sd, __u16 nlmsg_type, __u32 nlmsg_pid,
+            __u8 genl_cmd, __u16 nla_type,
+            void *nla_data, int nla_len)

 {
 {

-    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;
+       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
  */
 int get_family_id(int sd)
 {
 /*
  * 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;
-}
+       struct {
+               struct nlmsghdr n;
+               struct genlmsghdr g;
+               char buf[256];
+       } ans;
+
+       int id, 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);
+
+       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;

 
 

-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);
+       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 sigchld(int sig)
+void print_delayacct(struct taskstats *t)

 {
 {

-    done = 1;
+       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);

 }
 
 int main(int argc, char *argv[])
 {
 }
 
 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;
+       int c, rc, rep_len, aggr_len, len2, cmd_type;
+       __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[128];
+       int loop = 0;
+
+       struct msgtemplate msg;
+
+       while (1) {
+               c = getopt(argc, argv, "dw:r:m:t:p:v:l");
+               if (c < 0)
+                       break;

 
 

-    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);
+               switch (c) {
+               case 'd':
+                       printf("print delayacct stats ON\n");
+                       print_delays = 1;
+                       break;
+               case 'w':
+                       strncpy(logfile, optarg, MAX_FILENAME);
+                       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));
+                       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;
+                       print_delays = 1;
+                       break;
+               case 'p':
+                       tid = atoi(optarg);
+                       if (!tid)
+                               err(1, "Invalid pid\n");
+                       cmd_type = TASKSTATS_CMD_ATTR_PID;
+                       print_delays = 1;
+                       break;
+               case 'v':
+                       printf("debug on\n");
+                       dbg = 1;
+                       break;
+               case 'l':
+                       printf("listen forever\n");
+                       loop = 1;
+                       break;
+               default:
+                       printf("Unknown option %d\n", c);
+                       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");
+       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);
+               }
+       }

 
 

-    act.sa_handler = SIG_IGN;
-    sigemptyset(&act.sa_mask);
-    if (sigaction(SIGINT, &act, NULL) < 0)
-       err(1, "sigaction failed for SIGINT\n");
+       if ((nl_sd = create_nl_socket(NETLINK_GENERIC)) < 0)
+               err(1, "error creating Netlink socket\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;
+       mypid = getpid();
+       id = get_family_id(nl_sd);
+       if (!id) {
+               printf("Error getting family id, errno %d", errno);
+               goto err;

        }
        }

-
-       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);
+       PRINTF("family id %d\n", id);
+
+       if (maskset) {
+               rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
+                             TASKSTATS_CMD_ATTR_REGISTER_CPUMASK,
+                             &cpumask, sizeof(cpumask));
+               PRINTF("Sent register cpumask, retval %d\n", rc);
+               if (rc < 0) {
+                       printf("error sending register cpumask\n");
+                       goto err;
+               }

        }
 
        }
 

-       if (rep_len < 0) {
-           err(1, "error receiving reply message via Netlink\n");
-           break;
+       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) {
+                       printf("error sending tid/tgid cmd\n");
+                       goto done;
+               }

        }
 
        }
 

-       /* Validate response message */
-       if (!NLMSG_OK((&ans.n), rep_len))
-           err(1, "invalid reply message received via Netlink\n");
+       do {
+               int i;

 
 

-       rep_len = GENLMSG_PAYLOAD(&ans.n);
+               rep_len = recv(nl_sd, &msg, sizeof(msg), 0);
+               PRINTF("received %d bytes\n", rep_len);

 
 

-       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;
+               if (rep_len < 0) {
+                       printf("nonfatal reply error: errno %d\n", errno);
+                       continue;
+               }
+               if (msg.n.nlmsg_type == NLMSG_ERROR ||
+                   !NLMSG_OK((&msg.n), rep_len)) {
+                       printf("fatal reply error,  errno %d\n", errno);
+                       goto done;
+               }
+
+               PRINTF("nlmsghdr size=%d, 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;
+               i = 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 (fd) {
+                                                       if (write(fd, NLA_DATA(na), na->nla_len) < 0) {
+                                                               err(1,"write error\n");
+                                                       }
+                                               }
+                                               if (!loop)
+                                                       goto done;
+                                               break;
+                                       default:
+                                               printf("Unknown nested nla_type %d\n", na->nla_type);
+                                               break;
+                                       }
+                                       len2 += NLA_ALIGN(na->nla_len);
+                                       na = (struct nlattr *) ((char *) na + len2);
+                               }
+                               break;
+
+                       default:
+                               printf("Unknown nla_type %d\n", na->nla_type);
+                               break;

                        }
                        }

-                       break;
-                   }
-                   len2 += NLA_ALIGN(na->nla_len);
-                   na = (struct nlattr *) ((char *) na + len2);
-                   if (done)
-                       break;
+                       na = (struct nlattr *) (GENLMSG_DATA(&msg) + len);

                }
                }

-           }
-           na = (struct nlattr *) (GENLMSG_DATA(&ans) + len);
-           if (done)
-               break;
+       } while (loop);
+done:
+       if (maskset) {
+               rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
+                             TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK,
+                             &cpumask, sizeof(cpumask));
+               printf("Sent deregister mask, retval %d\n", rc);
+               if (rc < 0)
+                       err(rc, "error sending deregister cpumask\n");

        }
        }

-       if (done)
-           break;
-    }
-    while (1);
-
-    close(nl_sd);
-    return 0;
+err:
+       close(nl_sd);
+       if (fd)
+               close(fd);
+       return 0;

 }
 }

diff --git a/Documentation/accounting/taskstats.txt b/Documentation/accounting/taskstats.txt
index efd8f605bcd52fdf6b4d3fde71bd416593ea0006..92ebf29e9041cef2b68fc0c3c33698f8558ff085 100644 (file)
--- a/Documentation/accounting/taskstats.txt
+++ b/Documentation/accounting/taskstats.txt
@@ -26,20 +26,28 @@ leader - a process is deemed alive as long as it has any task belonging to it.
 Usage
 -----
 
 Usage
 -----
 

-To get statistics during task's lifetime, userspace opens a unicast netlink
+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).
 
 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, userspace opens a multicast
-netlink socket. Each time a task exits, its per-pid statistics is always sent
-by the kernel to each listener on the multicast socket. In addition, if it is
-the last thread exiting its thread group, an additional record containing the
-per-tgid stats are also sent. The latter contains the sum of per-pid stats for
-all threads in the thread group, both past and present.
+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
 
 getdelays.c is a simple utility demonstrating usage of the taskstats interface

-for reporting delay accounting statistics.
+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
 ---------
 
 Interface
 ---------


@@ -66,10 +74,20 @@ The messages are in the format
 
 The taskstats payload is one of the following three kinds:
 
 
 The taskstats payload is one of the following three kinds:
 

-1. Commands: Sent from user to kernel. The payload is 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.
+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:
 
 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:


@@ -138,4 +156,26 @@ 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.
 
 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.
+

 ----
 ----