linux-kernel - Re: [PATCH] perf: add support for per-event sampling period or frequency in perf record

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Date:	Tue, 23 Nov 2010 12:33:15 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, acme@...hat.com,
	paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com,
	robert.richter@....com
Subject: Re: [PATCH] perf: add support for per-event sampling period or
 frequency in perf record

On Tue, Nov 23, 2010 at 12:11 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-11-23 at 11:45 +0200, Stephane Eranian wrote:
>> This patch allows specifying a per event sampling period or frequency.
>> Up until now, the same sampling period or frequency was applied to all
>> the events specified on the command line of perf record. A sampling
>> period depends on the event, thus it is necessary to specify it per event.
>>
>> With this patch, both the -F and -c options now take a comma separated
>> list of values. If a value is omitted for an event, it defaults to 1000Hz
>> frequency mode as before.
>>
>> $ perf record -e cycles,instructions -c 100000,200000 -a -- sleep 5
>
>
> I remember an email not too long ago where people proposed to change the
> syntax so that:
>
>  -e evnt1,evnt2     -- create a group containing both events
>  -e evnt1 -e evnt2  -- create two separate events
>
Yes, that would be nice too especially for people interested in event ratios.

> It would be nice to make sure these two proposals will not interfere.
>
> Alternatively we extend the event syntax to include the period,
> something like:
>
>  -e evnt1:period=1234
>
Yes, that's the other approach. It may be more readable when you
have more events. I have that working with libpfm4, i.e., the full
event string is processed by the library. But for now, we could try
and do this in the tool as well, something like:

-e evtnt1:period=1234 -e evnt2:freq=100
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