Messages in this thread | | | Subject | Re: [PATCH] perf tools: fix: Force backward ring buffer mapped readonly | From | "Wangnan (F)" <> | Date | Thu, 12 Oct 2017 22:52:39 +0800 |
| |
On 2017/10/12 22:46, Wangnan (F) wrote: > > > 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. >
Sorry. I think removing it is reasonable now, but we need to solve the relationship between overwrite and backward first. I suggest remove the whole 'backward' concept, and makes evsels backward if it is overwrite. Is there any usecases that: 1. overwrite but not backward ring buffer: it will be unparsable after ring buffer full. 2. backward but not overwrite ring buffer: I don't see any advantage.
Thank you.
> Thank you.
| |