linux-kernel - Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide evsel

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Date:	Fri, 23 Oct 2015 13:17:49 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	pi3orama <pi3orama@....com>
Cc:	Wang Nan <wangnan0@...wei.com>, linux-kernel@...r.kernel.org,
	Alexei Starovoitov <ast@...mgrid.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [RFC PATCH] perf tools: Don't set inherit bit for system wide
 evsel

Em Fri, Oct 23, 2015 at 09:58:20PM +0800, pi3orama escreveu:
> 
> 
> 发自我的 iPhone
> 
> > 在 2015年10月23日，下午9:51，Arnaldo Carvalho de Melo <acme@...nel.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@...wei.com>
> >> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> >> Cc: Alexei Starovoitov <ast@...mgrid.com>
> >> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >> Cc: Li Zefan <lizefan@...wei.com>
> >> Cc: pi3orama@....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.

Yeah, we need to make it 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.

Ok, thanks in advance, lemme go back looking at eBPF :-)

- Arnaldo
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