linux-kernel - Re: [PATCH V6 08/17] perf tools: Add Intel PT support

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Date:	Fri, 26 Jun 2015 10:41:56 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V6 08/17] perf tools: Add Intel PT support

Em Fri, Jun 26, 2015 at 09:48:20AM +0300, Adrian Hunter escreveu:
> On 26/06/15 03:09, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Jun 25, 2015 at 08:56:34PM -0300, Arnaldo Carvalho de Melo escreveu:
> >> Will do the same tests with intel_pt as well, on a remote machine, add examples
> >> to the changeset logs and everything going well, aim for pushing for Ingo soon,
> > 
> > So, I asked for callchains, with:
> > 
> >  perf record -g -e intel_bts// ls
> > 
> > And it got stuck somewhere, then I did a perf top to see where it was,
> > and got to:
> > 
> >   96.24%  perf    [.] intel_bts_process_queue
> > 
> > Annotating I get to:
> > 
> >   1.17 │1a0:┌─→mov    0x8(%r13),%rdx
> >        │    │  test   %rdx,%rdx
> >  98.83 │    └──je     1a0
> > 
> > 
> > Which is an endless loop! Source code for intel_bts_process_buffer(),
> > inlined there:
> > 
> >         while (sz > sizeof(struct branch)) {
> >                 if (!branch->from && !branch->to)
> >                         continue;
> >                 err = intel_bts_synth_branch_sample(btsq, branch);
> >                 if (err)
> >                         break;
> >                 branch += 1;
> >                 sz -= sizeof(struct branch);
> >         }
> > 
> > Can you fix this, please, so that I can fold it into where it was
> > introduced, namely:
> > 
> > commit 439ad895a2aecea09416206f023336297cc72efe
> > Author: Adrian Hunter <adrian.hunter@...el.com>
> > Date:   Fri May 29 16:33:39 2015 +0300
> > 
> >     perf tools: Add Intel BTS support
> 
> It is fixed as an unexpected side-effect of a following patch (which is probably why I didn't notice it - or perhaps I rolled the fix into the wrong patch O_o). The fix is in:
> 
>     perf tools: Output sample flags and insn_len from intel_bts
>     
>     intel_bts synthesizes samples.  Fill in the new flags and insn_len
>     members with instruction information.
>     
>     Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> 
> 
> So what you want is:
> 
> 
> diff --git a/tools/perf/util/intel-bts.c b/tools/perf/util/intel-bts.c
> index 48bcbd607ef7..68bb6fede55b 100644
> --- a/tools/perf/util/intel-bts.c
> +++ b/tools/perf/util/intel-bts.c
> @@ -304,7 +304,7 @@ static int intel_bts_process_buffer(struct intel_bts_queue *btsq,
>  				    struct auxtrace_buffer *buffer)
>  {
>  	struct branch *branch;
> -	size_t sz;
> +	size_t sz, bsz = sizeof(struct branch);
>  	int err = 0;
>  
>  	if (buffer->use_data) {
> @@ -318,14 +318,12 @@ static int intel_bts_process_buffer(struct intel_bts_queue *btsq,
>  	if (!btsq->bts->sample_branches)
>  		return 0;
>  
> -	while (sz > sizeof(struct branch)) {
> +	for (; sz > bsz; branch += 1, sz -= bsz) {
>  		if (!branch->from && !branch->to)
>  			continue;
>  		err = intel_bts_synth_branch_sample(btsq, branch);
>  		if (err)
>  			break;
> -		branch += 1;
> -		sz -= sizeof(struct branch);
>  	}
>  	return err;
>  }
> 
> 
> But obviously that will conflict with "perf tools: Output sample flags and insn_len from intel_bts"

I can fix those things up, to keep it bisectable, next time please try
to do it this way :-)

> Another thing, the intel_bts implementation does not support
> "instructions" samples because there is no timing information to
> use to create periodic samples.  But callchains are added only
> to "instructions" samples so there are no callchains in 'perf report'
> for intel_bts.  The call information is still available for

Humm, so IOW, what you say is that we should refuse to run 'record' when
asking for callchains and intel_bts?

> db-export and the example call-graph, though.

- Arnaldo
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