From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753295AbdJLOtU (ORCPT ); Thu, 12 Oct 2017 10:49:20 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:7989 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752757AbdJLOtS (ORCPT ); Thu, 12 Oct 2017 10:49:18 -0400 Subject: Re: [PATCH] perf tools: fix: Force backward ring buffer mapped readonly To: "Liang, Kan" , "linux-kernel@vger.kernel.org" , "acme@kernel.org" References: <20171012140052.5658-1-wangnan0@huawei.com> <37D7C6CF3E00A74B8858931C1DB2F077537D214F@SHSMSX103.ccr.corp.intel.com> <398e9843-bcae-4825-f7ca-5d1f92617cb0@huawei.com> <37D7C6CF3E00A74B8858931C1DB2F077537D27FA@SHSMSX103.ccr.corp.intel.com> <37D7C6CF3E00A74B8858931C1DB2F077537D2925@SHSMSX103.ccr.corp.intel.com> CC: Peter Zijlstra , Ingo Molnar , Jiri Olsa , Namhyung Kim , "Alexander Shishkin" , "Hunter, Adrian" , Andi Kleen , Li Zefan From: "Wangnan (F)" Message-ID: <1a46c859-13a1-ec6e-b27a-e54570ee8e11@huawei.com> Date: Thu, 12 Oct 2017 22:46:08 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F077537D2925@SHSMSX103.ccr.corp.intel.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.194.139] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090205.59DF80C9.00EA,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 669ead51551d4b5a5e0bb4556330ce6a Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>>>>> Cc: Liang Kan >>>>>> Cc: Arnaldo Carvalho de Melo >>>>>> Cc: Peter Zijlstra >>>>>> Cc: Ingo Molnar >>>>>> Cc: Jiri Olsa >>>>>> Cc: Namhyung Kim >>>>>> Cc: Alexander Shishkin >>>>>> Cc: Adrian Hunter >>>>>> Cc: Andi Kleen >>>>>> Cc: Li Zefan >>>>>> --- >>>>>> 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.