Messages in this thread Patch in this message | | | Subject | Re: A concern about overflow ring buffer mode | From | "Liang, Kan" <> | Date | Fri, 26 Oct 2018 15:07:40 -0400 |
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On 10/26/2018 3:02 PM, Arnaldo Carvalho de Melo wrote: > So, I'm adding the following to my tree to help in diagnosing problems > with this overwrite mode: >
Actually, you can use per-event overwrite term to disable overwrite mode for perf top.
/* * Check per-event overwrite term. * perf top should support consistent term for all events. * - All events don't have per-event term * E.g. "cpu/cpu-cycles/,cpu/instructions/" * Nothing change, return 0. * - All events have same per-event term * E.g. "cpu/cpu-cycles,no-overwrite/,cpu/instructions,no-overwrite/ * Using the per-event setting to replace the opts->overwrite if * they are different, then return 0. * - Events have different per-event term * E.g. "cpu/cpu-cycles,overwrite/,cpu/instructions,no-overwrite/" * Return -1 * - Some of the event set per-event term, but some not. * E.g. "cpu/cpu-cycles/,cpu/instructions,no-overwrite/" * Return -1 */ static int perf_top__overwrite_check(struct perf_top *top) {
Thanks, Kan
> > From 40feb09001c7cc2ba8aeaa0a8f03b6d28fa4ca95 Mon Sep 17 00:00:00 2001 > From: Arnaldo Carvalho de Melo <acme@redhat.com> > Date: Fri, 26 Oct 2018 15:55:23 -0300 > Subject: [PATCH 1/1] perf top: Allow disabling the overwrite mode > > In ebebbf082357 ("perf top: Switch default mode to overwrite mode") we > forgot to leave a way to disable that new default, add a --overwrite > option that can be disabled using --no-overwrite, since the code already > in such a way that we can readily disable this mode. > > This is useful when investigating bugs with this mode like the recent > report from David Miller where lots of unknown symbols appear due to > disabling the events while processing them which disables all record > types, not just PERF_RECORD_SAMPLE, which makes it impossible to resolve > maps when we lose PERF_RECORD_MMAP records. > > This can be easily seen while building a kernel, when there are lots of > short lived processes. > > Cc: Adrian Hunter <adrian.hunter@intel.com> > Cc: Andi Kleen <ak@linux.intel.com> > Cc: David Ahern <dsahern@gmail.com> > Cc: David Miller <davem@davemloft.net> > Cc: Jin Yao <yao.jin@linux.intel.com> > Cc: Jiri Olsa <jolsa@kernel.org> > Cc: Kan Liang <kan.liang@intel.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Wang Nan <wangnan0@huawei.com> > Link: https://lkml.kernel.org/n/tip-oqgsz2bq4kgrnnajrafcdhie@git.kernel.org > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> > --- > tools/perf/Documentation/perf-top.txt | 5 +++++ > tools/perf/builtin-top.c | 2 ++ > 2 files changed, 7 insertions(+) > > diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt > index 114fda12aa49..d4be6061fe1c 100644 > --- a/tools/perf/Documentation/perf-top.txt > +++ b/tools/perf/Documentation/perf-top.txt > @@ -242,6 +242,11 @@ Default is to monitor all CPUS. > --hierarchy:: > Enable hierarchy output. > > +--overwrite:: > + This is the default, but for investigating problems with it or any other strange > + behaviour like lots of unknown samples, we may want to disable this mode by using > + --no-overwrite. > + > --force:: > Don't do ownership validation. > > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c > index d21d8751e749..214fad747b04 100644 > --- a/tools/perf/builtin-top.c > +++ b/tools/perf/builtin-top.c > @@ -1372,6 +1372,8 @@ int cmd_top(int argc, const char **argv) > "Show raw trace event output (do not use print fmt or plugins)"), > OPT_BOOLEAN(0, "hierarchy", &symbol_conf.report_hierarchy, > "Show entries in a hierarchy"), > + OPT_BOOLEAN(0, "overwrite", &top.record_opts.overwrite, > + "Use a backward ring buffer, default: yes"), > OPT_BOOLEAN(0, "force", &symbol_conf.force, "don't complain, do it"), > OPT_UINTEGER(0, "num-thread-synthesize", &top.nr_threads_synthesize, > "number of thread to run event synthesize"), >
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