From b09c2364a4dc2a67e640c2b839d936302815693f Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Thu, 1 Mar 2018 14:52:50 -0300 Subject: perf record: Throttle user defined frequencies to the maximum allowed # perf record -F 200000 sleep 1 warning: Maximum frequency rate (15,000 Hz) exceeded, throttling from 200,000 Hz to 15,000 Hz. The limit can be raised via /proc/sys/kernel/perf_event_max_sample_rate. The kernel will lower it when perf's interrupts take too long. Use --strict-freq to disable this throttling, refusing to record. [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.019 MB perf.data (15 samples) ] # perf evlist -v cycles:ppp: size: 112, { sample_period, sample_freq }: 15000, sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1 For those wanting that it fails if the desired frequency can't be used: # perf record --strict-freq -F 200000 sleep 1 error: Maximum frequency rate (15,000 Hz) exceeded. Please use -F freq option with a lower value or consider tweaking /proc/sys/kernel/perf_event_max_sample_rate. # Suggested-by: Ingo Molnar Cc: Adrian Hunter Cc: David Ahern Cc: Jiri Olsa Cc: Namhyung Kim Cc: Wang Nan Link: https://lkml.kernel.org/n/tip-oyebruc44nlja499nqkr1nzn@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/record.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) (limited to 'tools/perf/util') diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c index acabf54ceccb..4f1a82e76d39 100644 --- a/tools/perf/util/record.c +++ b/tools/perf/util/record.c @@ -216,11 +216,21 @@ static int record_opts__config_freq(struct record_opts *opts) * User specified frequency is over current maximum. */ if (user_freq && (max_rate < opts->freq)) { - pr_err("Maximum frequency rate (%u) reached.\n" - "Please use -F freq option with lower value or consider\n" - "tweaking /proc/sys/kernel/perf_event_max_sample_rate.\n", - max_rate); - return -1; + if (opts->strict_freq) { + pr_err("error: Maximum frequency rate (%'u Hz) exceeded.\n" + " Please use -F freq option with a lower value or consider\n" + " tweaking /proc/sys/kernel/perf_event_max_sample_rate.\n", + max_rate); + return -1; + } else { + pr_warning("warning: Maximum frequency rate (%'u Hz) exceeded, throttling from %'u Hz to %'u Hz.\n" + " The limit can be raised via /proc/sys/kernel/perf_event_max_sample_rate.\n" + " The kernel will lower it when perf's interrupts take too long.\n" + " Use --strict-freq to disable this throttling, refusing to record.\n", + max_rate, opts->freq, max_rate); + + opts->freq = max_rate; + } } /* -- cgit v1.2.3-70-g09d2