linux-kernel - Re: [PATCH] perf cs-etm: Correct CPU mode for samples

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Message-ID: <20181030151137.GF23310@kernel.org>
Date:   Tue, 30 Oct 2018 12:11:38 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     leo.yan@...aro.org, Adrian Hunter <adrian.hunter@...el.com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Coresight ML <coresight@...ts.linaro.org>
Subject: Re: [PATCH] perf cs-etm: Correct CPU mode for samples

Em Tue, Oct 30, 2018 at 11:04:49PM +0800, leo.yan@...aro.org escreveu:
> Hi Arnaldo,
> 
> On Tue, Oct 30, 2018 at 11:32:26AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Oct 30, 2018 at 03:18:28PM +0800, Leo Yan escreveu:
> > > Since commit 9042f5e3539e ("perf tools: Stop fallbacking to kallsyms
> > > for vdso symbols lookup"), the kernel address cannot be properly parsed
> > > to kernel symbol with command 'perf script -k vmlinux'.  The reason is
> > > CoreSight samples is always to set CPU mode as PERF_RECORD_MISC_USER,
> > > thus it fails to find corresponding map/dso in below flows:
> > > 
> > >   process_sample_event()
> > >     `-> machine__resolve()
> > > 	  `-> thread__find_map(thread, sample->cpumode, sample->ip, al);
> > > 
> > > In this flow it needs to pass argument 'sample->cpumode' to tell what's
> > > the CPU mode, before it always passed PERF_RECORD_MISC_USER but without
> > > any failure until the commit 9042f5e3539e ("perf tools: Stop fallbacking
> > > to kallsyms for vdso symbols lookup") has been merged.  The reason is
> > > even with the wrong CPU mode the function thread__find_map() firstly
> > > fails to find map but it will rollback to find kernel map for vdso
> > > symbols lookup.  In the latest code it has removed the fallback code,
> > > thus if CPU mode is PERF_RECORD_MISC_USER then it cannot find map
> > > anymore with kernel address.
> > > 
> > > This patch is to correct samples CPU mode setting, it creates a new
> > > helper function cs_etm__cpu_mode() to tell what's the CPU mode based on
> > > the address with the info from machine structure; this patch has a bit
> > > extension to check not only kernel and user mode, but also check for
> > > host/guest and hypervisor mode.  Finally this patch uses the function
> > > in instruction and branch samples and also apply in cs_etm__mem_access()
> > > for a minor polishing.
> > 
> > Mathieu, can I have your Acked-by, please? Leo, thanks for acting so
> > quickly on this one! 
> 
> Thanks for reivewing.  Yeah, let's wait for Mathieu reviewing as well,
> as I know he is travelling so might be delay a bit.

I'm tentatively applying the patch, as this needs fixing ASAP, and I
take that you have tested it and it cured the problem for you, so should
be a good indication for the acceptance of the patch.

We can always fix some detail later.
 
> Just remind, we might need the similiar change for util/intel-pt.c and
> util/intel-bts.c when generate samples, otherwise they might have the
> same regression for kernel symbols.  I am not the best person to change
> these two files, but bring up this for attention.

Right, I think Adrian is working on it, Adrian?
 
> > Now processing coresight traces should be faster, less lookups :-)
> 
> Thanks!

- Arnaldo