Messages in this thread | | | Date | Fri, 26 Oct 2018 16:12:31 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: A concern about overflow ring buffer mode |
| |
Em Fri, Oct 26, 2018 at 03:07:40PM -0400, Liang, Kan escreveu: > 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) > {
I see, it will disable that opts->overwrite if it finds the no-overwrite in the per-event definition, so the equivalent of the option I added below:
perf top --no-overwrite
is:
perf top -e cycles/no-overwrite/
I checked and both have the same result. But I still think there is value in having the shorter form, ok?
- Arnaldo
> 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"), > >
| |