From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: george@mvista.com, johnstul@us.ibm.com
Cc: linux-kernel@vger.kernel.org, michel.dagenais@polymtl.ca
Subject: [patch] i386 and x86_64 TSC set_cyc2ns_scale imprecision
Date: Mon, 12 Sep 2005 13:27:27 -0400 [thread overview]
Message-ID: <20050912172727.GA30644@Krystal> (raw)
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Hi,
I just found out that some precision is unnecessarily lost in the
arch/i386/kernel/timers/timer_tsc.c:set_cyc2ns_scale function. It uses a
cpu_mhz parameter when it could use a cpu_khz. In the specific case of an Intel
P4 running at 3001.171 Mhz, the truncation to 3001 Mhz leads to an imprecision
of 19 microseconds per second : this is very sad for a timer with nearly
nanosecond accuracy.
The patch for 2.6.13.1 is attached. It patches the x86_64 architecture too.
Please look at the patch for further comments.
Mathieu Desnoyers
Master Student in Computer Engineering
École Polytechnique de Montréal
OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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reply other threads:[~2005-09-12 17:27 UTC|newest]
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