Messages in this thread | | | Subject | Re: [PATCH] perf tools: fix: Force backward ring buffer mapped readonly | From | "Wangnan (F)" <> | Date | Thu, 12 Oct 2017 22:46:08 +0800 |
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On 2017/10/12 22:45, Liang, Kan wrote: >> On 2017/10/12 20:56, Liang, Kan wrote: >>>> On 2017/10/11 21:16, Liang, Kan wrote: >>>>>> perf record's --overwrite option doesn't work as we expect. >>>>>> For example: >>>> [SNIP] >>>> >>>>>> In the above example we get same records from the backward ring >>>>>> buffer all the time. Overwriting is not triggered. >>>>>> >>>>>> This commit maps backward ring buffers readonly, make it overwritable. >>>>>> It is safe because we assume backward ring buffer always overwritable >>>>>> in other part of code. >>>>>> >>>>>> After applying this patch: >>>>>> >>>>>> $ ~/linux/tools/perf$ sudo ./perf record -m 4 -e raw_syscalls:* >>>>>> -g -- overwrite \ >>>>>> --switch-output=1s --tail-synthesize dd >>>>>> if=/dev/zero of=/dev/null >>>> [SNIP] >>>> >>>>>> Signed-off-by: Wang Nan <wangnan0@huawei.com> >>>>>> Cc: Liang Kan <kan.liang@intel.com> >>>>>> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> >>>>>> Cc: Peter Zijlstra <peterz@infradead.org> >>>>>> Cc: Ingo Molnar <mingo@kernel.org> >>>>>> Cc: Jiri Olsa <jolsa@kernel.org> >>>>>> Cc: Namhyung Kim <namhyung@kernel.org> >>>>>> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> >>>>>> Cc: Adrian Hunter <adrian.hunter@intel.com> >>>>>> Cc: Andi Kleen <ak@linux.intel.com> >>>>>> Cc: Li Zefan <lizefan@huawei.com> >>>>>> --- >>>>>> tools/perf/util/evlist.c | 7 ++++++- >>>>>> 1 file changed, 6 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c >>>>>> index c6c891e..a86b0d2 100644 >>>>>> --- a/tools/perf/util/evlist.c >>>>>> +++ b/tools/perf/util/evlist.c >>>>>> @@ -799,12 +799,14 @@ perf_evlist__should_poll(struct perf_evlist >>>>>> *evlist __maybe_unused, >>>>>> } >>>>>> >>>>>> static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int >> idx, >>>>>> - struct mmap_params *mp, int cpu_idx, >>>>>> + struct mmap_params *_mp, int cpu_idx, >>>>>> int thread, int *_output, int >>>>>> *_output_backward) >>>>>> { >>>>>> struct perf_evsel *evsel; >>>>>> int revent; >>>>>> int evlist_cpu = cpu_map__cpu(evlist->cpus, cpu_idx); >>>>>> + struct mmap_params *mp = _mp; >>>>>> + struct mmap_params backward_mp; >>>>>> >>>>>> evlist__for_each_entry(evlist, evsel) { >>>>>> struct perf_mmap *maps = evlist->mmap; @@ -815,6 +817,9 >>>> @@ static >>>>>> int perf_evlist__mmap_per_evsel(struct >>>>>> perf_evlist *evlist, int idx, >>>>>> if (evsel->attr.write_backward) { >>>>>> output = _output_backward; >>>>>> maps = evlist->backward_mmap; >>>>>> + backward_mp = *mp; >>>>>> + backward_mp.prot &= ~PROT_WRITE; >>>>>> + mp = &backward_mp; >>>>>> >>>>>> if (!maps) { >>>>>> maps = perf_evlist__alloc_mmap(evlist); >>>>> So it's trying to support per-event overwrite. >>>>> How about the global --overwrite option? >>>> Not only the per-event overwrite. See the example above. The overall -- >>>> overwrite option is also respected. In perf_evsel__config, per-event evsel >>>> 'backward' setting is set based on overall '--overwrite' and per-event >>>> '/overwrite/' setting. >>> But how about evlist->overwrite? I think it still keeps the wrong setting. >>> The overwrite is implicitly applied. Some settings are inconsistent. >>> >>> Is there any drawback if you use opts->overwrite for >> perf_evlist__mmap_ex? >> >> We will always face such inconsistency, because we have >> an /no-overwrite/ option which can be set per-evsel. >> Setting evlist->overwrite won't make things more consistent, >> because in a evlist, different evsel can have different >> overwrite setting. A simple solution is making evlist >> non-overwrite by default, and watch all overwrite evsels >> a special cases. Then we have only 2 cases to consider: >> >> 1. overwrite evsel in a non-overwrite evlist. >> 2. non-overwrite evsel in a non-overwrite evlist. >> > If evlist->overwrite is always non-overwrite, why not remove it? >
Some testcases require it.
Thank you.
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