From 30626e0844757b7b371353eb693354c4ccc5eb0e Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Tue, 2 Feb 2021 18:01:16 +0900 Subject: [PATCH] perf tools: Use /proc//task//status for PERF_RECORD_ event synthesis To save memory usage, it needs to reduce the number of entries in the proc filesystem. It's using /proc//task directory to traverse threads in the process and then kernel creates /proc//task/ entries. After that it checks the thread info using the /proc//status file rather than /proc//task//status. As far as I can see, they are the same and contain all the info we need. Using the latter eliminates the unnecessary /proc/ entry. This can be useful especially a large number of threads are used in the system. In my experiment around 1KB of memory on average was saved for each thread (which is not a thread group leader). To do this, pass both pid and tid to perf_event_prepare_comm() if it knows them. In case it doesn't know, passing 0 as pid will do the old way. Signed-off-by: Namhyung Kim Acked-by: Jiri Olsa Cc: Alexander Shishkin Cc: Andi Kleen Cc: Ian Rogers Cc: Ingo Molnar Cc: Mark Rutland Cc: Peter Zijlstra Cc: Stephane Eranian Link: https://lore.kernel.org/r/20210202090118.2008551-2-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/synthetic-events.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c index 3a89852..0cc9986 100644 --- a/tools/perf/util/synthetic-events.c +++ b/tools/perf/util/synthetic-events.c @@ -69,7 +69,7 @@ int perf_tool__process_synth_event(struct perf_tool *tool, * 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, +static int perf_event__get_comm_ids(pid_t pid, pid_t tid, char *comm, size_t len, pid_t *tgid, pid_t *ppid) { char bf[4096]; @@ -81,7 +81,10 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len, *tgid = -1; *ppid = -1; - snprintf(bf, sizeof(bf), "/proc/%d/status", pid); + if (pid) + snprintf(bf, sizeof(bf), "/proc/%d/task/%d/status", pid, tid); + else + snprintf(bf, sizeof(bf), "/proc/%d/status", tid); fd = open(bf, O_RDONLY); if (fd < 0) { @@ -93,7 +96,7 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len, close(fd); if (n <= 0) { pr_warning("Couldn't get COMM, tigd and ppid for pid %d\n", - pid); + tid); return -1; } bf[n] = '\0'; @@ -116,27 +119,27 @@ static int perf_event__get_comm_ids(pid_t pid, char *comm, size_t len, memcpy(comm, name, size); comm[size] = '\0'; } else { - pr_debug("Name: string not found for pid %d\n", pid); + pr_debug("Name: string not found for pid %d\n", tid); } if (tgids) { tgids += 5; /* strlen("Tgid:") */ *tgid = atoi(tgids); } else { - pr_debug("Tgid: string not found for pid %d\n", pid); + pr_debug("Tgid: string not found for pid %d\n", tid); } if (ppids) { ppids += 5; /* strlen("PPid:") */ *ppid = atoi(ppids); } else { - pr_debug("PPid: string not found for pid %d\n", pid); + pr_debug("PPid: string not found for pid %d\n", tid); } return 0; } -static int perf_event__prepare_comm(union perf_event *event, pid_t pid, +static int perf_event__prepare_comm(union perf_event *event, pid_t pid, pid_t tid, struct machine *machine, pid_t *tgid, pid_t *ppid) { @@ -147,7 +150,7 @@ static int perf_event__prepare_comm(union perf_event *event, pid_t pid, memset(&event->comm, 0, sizeof(event->comm)); if (machine__is_host(machine)) { - if (perf_event__get_comm_ids(pid, event->comm.comm, + if (perf_event__get_comm_ids(pid, tid, event->comm.comm, sizeof(event->comm.comm), tgid, ppid) != 0) { return -1; @@ -168,7 +171,7 @@ static int perf_event__prepare_comm(union perf_event *event, pid_t pid, event->comm.header.size = (sizeof(event->comm) - (sizeof(event->comm.comm) - size) + machine->id_hdr_size); - event->comm.tid = pid; + event->comm.tid = tid; return 0; } @@ -180,7 +183,7 @@ pid_t perf_event__synthesize_comm(struct perf_tool *tool, { pid_t tgid, ppid; - if (perf_event__prepare_comm(event, pid, machine, &tgid, &ppid) != 0) + if (perf_event__prepare_comm(event, 0, pid, machine, &tgid, &ppid) != 0) return -1; if (perf_tool__process_synth_event(tool, event, machine, process) != 0) @@ -746,7 +749,7 @@ static int __event__synthesize_thread(union perf_event *comm_event, continue; rc = -1; - if (perf_event__prepare_comm(comm_event, _pid, machine, + if (perf_event__prepare_comm(comm_event, pid, _pid, machine, &tgid, &ppid) != 0) break; -- 2.7.4