*
* Copyright (C) Shailabh Nagar, IBM Corp. 2005
* Copyright (C) Balbir Singh, IBM Corp. 2006
+ * Copyright (c) Jay Lan, SGI. 2006
*
*/
#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
*/
-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)
{
- 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 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;
}
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).
-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
-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
---------
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:
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.
+
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git://ftp.safe.ca / safe / jmp / linux-2.6 / commitdiff