From: Paul Clarke <pc@us.ibm.com>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: "linux-perf-users@vger.kernel.org"
<linux-perf-users@vger.kernel.org>,
Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
Will Deacon <Will.Deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>,
Jiri Olsa <jolsa@redhat.com>
Subject: Re: perf event grouping for dummies (was Re: [PATCH] arc: perf: Enable generic "cache-references" and "cache-misses" events)
Date: Wed, 21 Sep 2016 19:43:28 -0500 [thread overview]
Message-ID: <04f6dcd2-35c6-6e28-2dcf-bc5f0bb446dc@us.ibm.com> (raw)
In-Reply-To: <2a18ae06-3abd-c3a1-e980-f04c511b08e5@synopsys.com>
On 09/20/2016 03:56 PM, Vineet Gupta wrote:
> On 09/01/2016 01:33 AM, Peter Zijlstra wrote:
>>> - is that what perf event grouping is ?
>>
>> Again, nope. Perf event groups are single counter (so no implicit
>> addition) that are co-scheduled on the PMU.
>
> I'm not sure I understand - does this require specific PMU/arch support - as in
> multiple conditions feeding to same counter.
My read is that is that what Peter meant was that each event in the perf event group is a single counter, so all the events in the group are counted simultaneously. (No multiplexing.)
>> You can do it like:
>>
>> perf stat -e '{cycles,instructions}'
>>
>> Which will place the cycles event and the instructions event in a group
>> and thereby guarantee they're co-scheduled.
>
> Again when you say co-scheduled what do you mean - why would anyone use the event
> grouping - is it when they only have 1 counter and they want to count 2
> conditions/events at the same time - isn't this same as event multiplexing ?
I'd say it's the converse of multiplexing. Instead of mapping multiple events to a single counter, perf event groups map a set of events each to their own counter, and they are active simultaneously. I suppose it's possible for the _groups_ to be multiplexed with other events or groups, but the group as a whole will be scheduled together, as a group.
If you have a single counter, I don't believe you can support perf event groups, by definition.
Regards,
Paul Clarke, IBM
next prev parent reply other threads:[~2016-09-22 0:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-25 11:47 [PATCH] arc: perf: Enable generic "cache-references" and "cache-misses" events Alexey Brodkin
2016-08-26 17:30 ` Vineet Gupta
2016-08-31 19:05 ` Vineet Gupta
2016-09-01 8:33 ` Peter Zijlstra
2016-09-20 20:56 ` perf event grouping for dummies (was Re: [PATCH] arc: perf: Enable generic "cache-references" and "cache-misses" events) Vineet Gupta
2016-09-22 0:43 ` Paul Clarke [this message]
2016-09-22 7:56 ` Peter Zijlstra
2016-09-22 17:50 ` Vineet Gupta
2016-09-22 18:23 ` Paul Clarke
2016-09-22 19:42 ` Arnaldo Carvalho de Melo
2016-09-14 17:53 ` [PATCH] arc: perf: Enable generic "cache-references" and "cache-misses" events Vineet Gupta
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