linux-kernel - [RFC patch 00/18] Trace Clock v2

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Message-Id: <20081107052336.652868737@polymtl.ca>
Date:	Fri, 07 Nov 2008 00:23:36 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: [RFC patch 00/18] Trace Clock v2

Hi,

I've cleaned up the LTTng timestamping code, renamed it into "trace clock",
ripped apart the tsc_sync.c x86 code, added documentation (printk to the console
when the tracing clock is used) about what to do when an unsync TSC is detected.
I however kept the cache-line bouncing workaround for now. However, I now
synchronize the counters every jiffy with a per-cpu timer so it gives an upper
bound to the time imprecision.

The trace clock works with a trace_clock_get()/put(), so all the mechanic and
overhead that might be required to provide correct timestamps on weird systems
is *only* enabled when tracing is active.

I plan to stick to this simple solution for now so we can get reliable tracing
for 95ish% of systems out there, and to keep room for improvement (nice NTP-like
schemes) for a later version. (sadly, given this is actually v2, I cannot say
"let's keep that for v2") ;)

This patchset applies on top of 2.6.28-rc3.

Mathieu

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Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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