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SubjectRe: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel
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发自我的 iPhone

> 在 2015年10月23日,下午9:51,Arnaldo Carvalho de Melo <acme@kernel.org> 写道:
>
> Em Fri, Oct 23, 2015 at 10:43:49AM +0000, Wang Nan escreveu:
>> Inherit bit is useless for a system wide evsel [1]. Further kernel
>> improvements are giving more constrain [2] on inherit events. This
>> patch set inherit bit to 0 to avoid potential constrains.
>>
>> [1] http://lkml.kernel.org/r/20151022124142.GQ17308@twins.programming.kicks-ass.net
>> [2] http://lkml.kernel.org/r/1445559014-4667-1-git-send-email-ast@kernel.org
>>
>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
>> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
>> Cc: Alexei Starovoitov <ast@plumgrid.com>
>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>> Cc: Li Zefan <lizefan@huawei.com>
>> Cc: pi3orama@163.com
>> Link: http://lkml.kernel.org/n/ebpf-0tgilipxoo6fiebcxu3ft866@git.kernel.org
>> ---
>>
>> evsel->system_wide doesn't correct reflect whether this evsel is system
>> wide or not, so checks pid when invoking perf_event_open, and it is
>> always correct.
>
> Can't we do this at perf_evlist__config() or perf_evsel__config() time?

perf_evlist_config() is excluded because perf record doesn't use it.

>
> We have record_opts at perf_evsel__config() time and I think we should
> leave changing the attr at perf_evsel__open() time for feature
> fallbacks, i.e. something we will only know when trying to use, which is
> different from this inherit-on-syswide case, that we know far in advance
> we will not need.

I tried to set this bit based on evsel->system_wide but it seems not reliable
as it should be, so I was wondering whether it is designed for other use. I will look
into this next week.

Thank you.
>
> - Arnaldo
>
>> ---
>> tools/perf/util/evsel.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 5566b16..e2d6c9a 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -1337,6 +1337,7 @@ retry_sample_id:
>>
>> for (thread = 0; thread < nthreads; thread++) {
>> int group_fd;
>> + struct perf_event_attr attr;
>>
>> if (!evsel->cgrp && !evsel->system_wide)
>> pid = thread_map__pid(threads, thread);
>> @@ -1346,7 +1347,10 @@ retry_open:
>> pr_debug2("sys_perf_event_open: pid %d cpu %d group_fd %d flags %#lx\n",
>> pid, cpus->map[cpu], group_fd, flags);
>>
>> - FD(evsel, cpu, thread) = sys_perf_event_open(&evsel->attr,
>> + attr = evsel->attr;
>> + if (pid == -1)
>> + attr.inherit = 0;
>> + FD(evsel, cpu, thread) = sys_perf_event_open(&attr,
>> pid,
>> cpus->map[cpu],
>> group_fd, flags);
>> --
>> 1.8.3.4



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