linux-kernel - Re: [PATCH 2/3] perf/x86/intel/pt: Add an option to not force PSB+ on every schedule-in

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Date:	Thu, 30 Jul 2015 16:36:42 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	adrian.hunter@...el.com, x86@...nel.org, hpa@...or.com,
	acme@...radead.org
Subject: Re: [PATCH 2/3] perf/x86/intel/pt: Add an option to not force PSB+ on every schedule-in

Alexander Shishkin <alexander.shishkin@...ux.intel.com> writes:

> It kinda does make a difference: inside PSB+ you get a TSC packet, which
> carries the tsc timestamp as a payload, so, with the current behavior,
> since you'll get one of those at every event schedule-in, you'll have
> many more time synchronization points with the perf stream, but when the
> default changes, suddenly your timestamps way further apart and the
> decoder needs to put in additional guesswork to correlate those MMAP
> events in the perf stream with the PT trace.

I spoke hastily, TSC packets will be generated on every schedule-in (as
well as other packets that normally come in PSB+) regardless of the
actual PSB, so scratch the above. Let me replace the above with a
smaller patch.

Regards,
--
Alex
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