linux-kernel - Re: [PATCH 2/9] x86, perf: Add support for PEBSv3 profiling

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Message-ID: <20150508115954.GT2366@two.firstfloor.org>
Date:	Fri, 8 May 2015 13:59:54 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, kan.liang@...el.com,
	eranian@...gle.com, acme@...radead.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/9] x86, perf: Add support for PEBSv3 profiling

> That's wrong. It does not respect perf_event_attr::clock_id.

Ok.

Are we really defaulting to real time now? (CLOCK_REALTIME == 0)
What happens when ntpd is active and lets the time drift? That
sounds very bad for event accuracy.

The clockid patch looks broken to me. At least it should default
to MONOTONIC time, not just the time that happens to be 0 by 
accident.

Also I question we really need that many different kinds of
time stamps.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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