linux-kernel - Re: [PATCH 4/7] perf/x86-ibs: Add support for IBS pseudo events

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Message-ID: <1336395782.27020.37.camel@laptop>
Date:	Mon, 07 May 2012 15:03:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Robert Richter <robert.richter@....com>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] perf/x86-ibs: Add support for IBS pseudo events

On Wed, 2012-05-02 at 20:26 +0200, Robert Richter wrote:
> +enum ibs_filter_type {
> +       IBS_NO_FILTER           = 0,
> +       IBS_MATCH_FILTER        = 1,
> +       IBS_ANY_SET_FILTER      = 2,
> +       IBS_PSEUDO_EVENT        = 0x0F,
> +};

I don't get how those pseudo events work, AFAIKT IBS_PSEUDO_EVENT causes
one to loose all events since it does have a filter set but fails the
filter and thus we skip the call to perf_event_overflow().

Furthermore, I think this filter stuff should accumulate the period so
that PERF_SAMPLE_PERIOD still works correctly and reflects the number of
counts since the last sample.

Also, what's the point of filtering in-kernel as opposed to doing all
this in userspace? Is the amount of data 'saved' significant enough?

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