From: Arun Sharma <asharma@fb.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Mike Galbraith <efault@gmx.de>, Paul Mackerras <paulus@samba.org>,
Peter Zijlstra <peterz@infradead.org>,
Stephane Eranian <eranian@google.com>,
Namhyung Kim <namhyung.kim@lge.com>,
Tom Zanussi <tzanussi@gmail.com>,
linux-perf-users@vger.kernel.org
Subject: Re: [PATCH] perf: Add a new sort order: SORT_INCLUSIVE (v4)
Date: Tue, 27 Mar 2012 11:09:48 -0700 [thread overview]
Message-ID: <4F72026C.3050604@fb.com> (raw)
In-Reply-To: <20120325021451.GA14971@somewhere.redhat.com>
On 3/24/12 7:14 PM, Frederic Weisbecker wrote:
>> The other problem in branch stacks/LBR is that they're
>> sampled branches. Just because I got a sample with:
>>
>> a -> b
>> b -> c
>>
>> doesn't necessarily mean that the callchain was a -> b -> c.
>
> Not sure what you mean. If you have a -> b, b -> c in single
> LBR sample it means you got a -> b -> c.
>
I was going by Stephane's commit message here:
http://article.gmane.org/gmane.linux.kernel/1236999
> Statistical sampling of taken branch should not be confused
> for branch tracing. Not all branches are necessarily captured
Stephane, could you please explain if the 16 filtered branches in LBR
are guaranteed to be from a given callchain to the leaf function? My
understanding is that it's not.
callchain1: a -> b -> d -> e (sample a->b)
callchain2: a -> c -> b -> f (sample b->f)
on PMU interrupt can we end up with:
b -> f <- top of stack
a -> b
...
even though a -> b -> f can never happen in the actual program flow?
-Arun
WARNING: multiple messages have this Message-ID (diff)
From: Arun Sharma <asharma@fb.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
"Arnaldo Carvalho de Melo" <acme@redhat.com>,
Mike Galbraith <efault@gmx.de>,
"Paul Mackerras" <paulus@samba.org>,
Peter Zijlstra <peterz@infradead.org>,
"Stephane Eranian" <eranian@google.com>,
Namhyung Kim <namhyung.kim@lge.com>,
"Tom Zanussi" <tzanussi@gmail.com>,
<linux-perf-users@vger.kernel.org>
Subject: Re: [PATCH] perf: Add a new sort order: SORT_INCLUSIVE (v4)
Date: Tue, 27 Mar 2012 11:09:48 -0700 [thread overview]
Message-ID: <4F72026C.3050604@fb.com> (raw)
In-Reply-To: <20120325021451.GA14971@somewhere.redhat.com>
On 3/24/12 7:14 PM, Frederic Weisbecker wrote:
>> The other problem in branch stacks/LBR is that they're
>> sampled branches. Just because I got a sample with:
>>
>> a -> b
>> b -> c
>>
>> doesn't necessarily mean that the callchain was a -> b -> c.
>
> Not sure what you mean. If you have a -> b, b -> c in single
> LBR sample it means you got a -> b -> c.
>
I was going by Stephane's commit message here:
http://article.gmane.org/gmane.linux.kernel/1236999
> Statistical sampling of taken branch should not be confused
> for branch tracing. Not all branches are necessarily captured
Stephane, could you please explain if the 16 filtered branches in LBR
are guaranteed to be from a given callchain to the leaf function? My
understanding is that it's not.
callchain1: a -> b -> d -> e (sample a->b)
callchain2: a -> c -> b -> f (sample b->f)
on PMU interrupt can we end up with:
b -> f <- top of stack
a -> b
...
even though a -> b -> f can never happen in the actual program flow?
-Arun
next prev parent reply other threads:[~2012-03-27 18:10 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-14 17:36 [PATCH] perf: Add a new sort order: SORT_INCLUSIVE (v4) Arun Sharma
2012-03-15 1:02 ` Namhyung Kim
2012-03-15 1:02 ` Namhyung Kim
2012-03-15 14:14 ` Frederic Weisbecker
2012-03-15 17:58 ` Arun Sharma
2012-03-15 17:58 ` Arun Sharma
2012-03-19 15:57 ` Frederic Weisbecker
2012-03-20 23:28 ` Arun Sharma
2012-03-20 23:28 ` Arun Sharma
2012-03-25 2:14 ` Frederic Weisbecker
2012-03-27 18:09 ` Arun Sharma [this message]
2012-03-27 18:09 ` Arun Sharma
2012-03-27 19:38 ` Peter Zijlstra
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