Messages in this thread | | | Subject | Re: A concern about overflow ring buffer mode | From | "Liang, Kan" <> | Date | Fri, 26 Oct 2018 15:16:29 -0400 |
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On 10/26/2018 3:12 PM, Arnaldo Carvalho de Melo wrote: > 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? >
Sure.
Thanks, Kan
> - 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"), >>>
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