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Date: Wed, 25 Mar 2015 15:15:26 -0400
From: Don Zickus <dzickus@...hat.com>
To: David Ahern <dsahern@...il.com>
Cc: acme@...nel.org, linux-kernel@...r.kernel.org,
Joe Mario <jmario@...hat.com>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events
On Wed, Mar 25, 2015 at 10:51:10AM -0600, David Ahern wrote:
> 363b785f38 added synthesized fork events and set a thread's parent id
> to itself. Since we are already processing /proc/<pid>/status the ppid
> can be determined properly. Make it so.
>
> Performance impact measured on a sparc based T5-8 (1024 CPUs):
> $ ps -efL | wc -l
> 20185
>
> Current code:
> $ time perf record -o perf-no-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
> mmap size 532480B
> [ perf record: Woken up 0 times to write data ]
> failed to write feature 9
> [ perf record: Captured and wrote 0.000 MB perf-no-ppid.data ]
>
> real 0m26.144s
> user 0m0.452s
> sys 0m25.564s
>
> With PPID patch:
> $ time ./perf_ppid record -o perf-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
> mmap size 532480B
> [ perf record: Woken up 0 times to write data ]
> failed to write feature 9
> [ perf record: Captured and wrote 0.000 MB perf-ppid.data ]
>
> real 0m25.743s
> user 0m0.268s
> sys 0m25.368s
>
> Signed-off-by: David Ahern <dsahern@...il.com>
> Cc: Don Zickus <dzickus@...hat.com>
> Cc: Joe Mario <jmario@...hat.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> ---
> v2:
> - removed loop in place of 1 read and processing a buffer
Hmm, I am not entirely sure this is correct. You made an optimization that
hides the negative impact your patch does. I would prefer you split this
patch into two pieces. One with the read loop optimization (which I think
is great) and the second is your ppid change.
I would then like to redo our test with the first patch applied and then
both patches applied.
I still think something is strange in the sense perf wasn't supposed to read
the /proc filesystem again for threads. It was supposed to inherit the
thread data from the parent (the original intent and big speed up of my
patch). I believe your patch breaks that and goes back to reading the /proc
filesystem again. :-( Though I haven't had a chance to figure out why.
Cheers,
Don
>
> tools/perf/util/event.c | 178 ++++++++++++++++++++++++++++++------------------
> 1 file changed, 110 insertions(+), 68 deletions(-)
>
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index d5efa5092ce6..e98cbba56033 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -49,70 +49,115 @@ static struct perf_sample synth_sample = {
> .period = 1,
> };
>
> -static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
> +/*
> + * Assumes that the first 4095 bytes of /proc/pid/stat contains
> + * the comm, tgid and ppid.
> + */
> +static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len,
> + pid_t *tgid, pid_t *ppid)
> {
> char filename[PATH_MAX];
> - char bf[BUFSIZ];
> - FILE *fp;
> - size_t size = 0;
> - pid_t tgid = -1;
> + char bf[4096];
> + int fd;
> + size_t size = 0, n;
> + char *nl, *name, *tgids, *ppids;
> +
> + *tgid = -1;
> + *ppid = -1;
>
> snprintf(filename, sizeof(filename), "/proc/%d/status", pid);
>
> - fp = fopen(filename, "r");
> - if (fp == NULL) {
> + fd = open(filename, O_RDONLY);
> + if (fd < 0) {
> pr_debug("couldn't open %s\n", filename);
> - return 0;
> + return -1;
> }
>
> - while (!comm[0] || (tgid < 0)) {
> - if (fgets(bf, sizeof(bf), fp) == NULL) {
> - pr_warning("couldn't get COMM and pgid, malformed %s\n",
> - filename);
> - break;
> - }
> -
> - if (memcmp(bf, "Name:", 5) == 0) {
> - char *name = bf + 5;
> - while (*name && isspace(*name))
> - ++name;
> - size = strlen(name) - 1;
> - if (size >= len)
> - size = len - 1;
> - memcpy(comm, name, size);
> - comm[size] = '\0';
> -
> - } else if (memcmp(bf, "Tgid:", 5) == 0) {
> - char *tgids = bf + 5;
> - while (*tgids && isspace(*tgids))
> - ++tgids;
> - tgid = atoi(tgids);
> - }
> + n = read(fd, bf, sizeof(bf) - 1);
> + close(fd);
> + if (n <= 0) {
> + pr_warning("Couldn't get COMM, tigd and ppid for pid %d\n",
> + pid);
> + return -1;
> }
> + bf[n] = '\0';
>
> - fclose(fp);
> + name = strstr(bf, "Name:");
> + tgids = strstr(bf, "Tgid:");
> + ppids = strstr(bf, "PPid:");
> +
> + if (name) {
> + name += 5; /* strlen("Name:") */
> +
> + while (*name && isspace(*name))
> + ++name;
> +
> + nl = strchr(name, '\n');
> + if (nl)
> + *nl = '\0';
> +
> + size = strlen(name);
> + if (size >= len)
> + size = len - 1;
> + memcpy(comm, name, size);
> + comm[size] = '\0';
> + } else
> + pr_debug("Name: string not found for pid %d\n", pid);
> +
> + if (tgids) {
> + tgids += 5; /* strlen("Tgid:") */
> + while (*tgids && isspace(*tgids))
> + ++tgids;
> +
> + nl = strchr(tgids, '\n');
> + if (nl)
> + *nl = '\0';
> +
> + *tgid = atoi(tgids);
> +
> + } else
> + pr_debug("Tgid: string not found for pid %d\n", pid);
> +
> + if (ppids) {
> + ppids += 5; /* strlen("PPid:") */
> +
> + while (*ppids && isspace(*ppids))
> + ++ppids;
> +
> + nl = strchr(ppids, '\n');
> + if (nl)
> + *nl = '\0';
> +
> + *ppid = atoi(ppids);
> + } else
> + pr_debug("PPid: string not found for pid %d\n", pid);
>
> - return tgid;
> + return 0;
> }
>
> -static pid_t perf_event__prepare_comm(union perf_event *event, pid_t pid,
> - struct machine *machine)
> +static int perf_event__prepare_comm(union perf_event *event, pid_t pid,
> + struct machine *machine,
> + pid_t *tgid, pid_t *ppid)
> {
> size_t size;
> - pid_t tgid;
> +
> + *ppid = -1;
>
> memset(&event->comm, 0, sizeof(event->comm));
>
> - if (machine__is_host(machine))
> - tgid = perf_event__get_comm_tgid(pid, event->comm.comm,
> - sizeof(event->comm.comm));
> - else
> - tgid = machine->pid;
> + if (machine__is_host(machine)) {
> + if (perf_event__get_comm_ids(pid, event->comm.comm,
> + sizeof(event->comm.comm),
> + tgid, ppid) != 0) {
> + return -1;
> + }
> + } else
> + *tgid = machine->pid;
>
> - if (tgid < 0)
> - goto out;
> + if (*tgid < 0)
> + return -1;
>
> - event->comm.pid = tgid;
> + event->comm.pid = *tgid;
> event->comm.header.type = PERF_RECORD_COMM;
>
> size = strlen(event->comm.comm) + 1;
> @@ -122,36 +167,35 @@ static pid_t perf_event__prepare_comm(union perf_event *event, pid_t pid,
> (sizeof(event->comm.comm) - size) +
> machine->id_hdr_size);
> event->comm.tid = pid;
> -out:
> - return tgid;
> +
> + return 0;
> }
>
> -static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
> - union perf_event *event, pid_t pid,
> - perf_event__handler_t process,
> - struct machine *machine)
> +static int perf_event__synthesize_comm(struct perf_tool *tool,
> + union perf_event *event, pid_t pid,
> + perf_event__handler_t process,
> + struct machine *machine,
> + pid_t *tgid, pid_t *ppid)
> {
> - pid_t tgid = perf_event__prepare_comm(event, pid, machine);
> -
> - if (tgid == -1)
> - goto out;
> + if (perf_event__prepare_comm(event, pid, machine, tgid, ppid) != 0)
> + return -1;
>
> if (process(tool, event, &synth_sample, machine) != 0)
> return -1;
>
> -out:
> - return tgid;
> + return 0;
> }
>
> static int perf_event__synthesize_fork(struct perf_tool *tool,
> - union perf_event *event, pid_t pid,
> - pid_t tgid, perf_event__handler_t process,
> + union perf_event *event,
> + pid_t pid, pid_t tgid, pid_t ppid,
> + perf_event__handler_t process,
> struct machine *machine)
> {
> memset(&event->fork, 0, sizeof(event->fork) + machine->id_hdr_size);
>
> - event->fork.ppid = tgid;
> - event->fork.ptid = tgid;
> + event->fork.ppid = ppid;
> + event->fork.ptid = ppid;
> event->fork.pid = tgid;
> event->fork.tid = pid;
> event->fork.header.type = PERF_RECORD_FORK;
> @@ -343,14 +387,12 @@ static int __event__synthesize_thread(union perf_event *comm_event,
> char filename[PATH_MAX];
> DIR *tasks;
> struct dirent dirent, *next;
> - pid_t tgid;
> + pid_t tgid, ppid;
>
> /* special case: only send one comm event using passed in pid */
> if (!full) {
> - tgid = perf_event__synthesize_comm(tool, comm_event, pid,
> - process, machine);
> -
> - if (tgid == -1)
> + if (perf_event__synthesize_comm(tool, comm_event, pid,
> + process, machine, &tgid, &ppid) != 0)
> return -1;
>
> return perf_event__synthesize_mmap_events(tool, mmap_event, pid, tgid,
> @@ -378,12 +420,12 @@ static int __event__synthesize_thread(union perf_event *comm_event,
> if (*end)
> continue;
>
> - tgid = perf_event__prepare_comm(comm_event, _pid, machine);
> - if (tgid == -1)
> + if (perf_event__prepare_comm(comm_event, _pid, machine,
> + &tgid, &ppid) != 0)
> return -1;
>
> if (perf_event__synthesize_fork(tool, fork_event, _pid, tgid,
> - process, machine) < 0)
> + ppid, process, machine) < 0)
> return -1;
> /*
> * Send the prepared comm event
> --
> 2.1.0
>
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