linux-kernel - Re: [PERF_EVENT 3.11] Group Multiplexing not Working Properly

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Message-ID: <CABPqkBTLdX=uFGFqO9NFS6Yiyn+ty5gNj6ta4LdtBBwnygOATA@mail.gmail.com>
Date:	Fri, 27 Jun 2014 16:17:21 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Luís Taniça <matallui@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PERF_EVENT 3.11] Group Multiplexing not Working Properly

Hi,

On Tue, Jun 24, 2014 at 7:36 PM, Luís Taniça <matallui@...il.com> wrote:
> Hi,
>
> I am trying to configure 8 events in a machine which supports only 4 (so, using multiplexing). I tried different approaches:
>
>         1) Configure 8 events independently (works as expected)
>         2) Configure 2 event-sets of 4 events each in counting mode (works as expected)
>         3) Configure 2 event-sets of 4 events each in sampling mode (not working right)
>
What do it mean 'not working' in 3)?
Are you using perf record or your own code?

I think it would help if you could share the exact setup, i.e., the various
struct perf_event_attr structs.

> In case 3) I also tried different approaches:
>
>         3.a) 1 ring-buffer for each event-set and a callback for the POLL signal
>                 - only the first ring-buffer was detecting samples
>                 - the second ring-buffer was empty
>
>         3.b) 1 ring-buffer shared between event-sets (using PERF_EVENT_IOC_SET_OUTPUT)
>                 - both event-sets were writing to the ring-buffer
>                 - 1st event-set only writes 2 samples while 2nd event-set writes like 20+ samples
>                 - samples from 1st event-set report time_enabled=time_running while samples from 2nd don’t
>
> Moreover, in both cases the wakeup_events parameter is not working.
> I believe there must be some programming bugs in perf_event while profiling in sampling mode with multiple event-sets (groups).
>
> Regards,
> matallui
>
>
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