From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Sun, 30 Oct 2005 22:59:25 +0000 (-0800)
Subject: [PATCH] i386 and x86_64 TSC set_cyc2ns_scale imprecision
X-Git-Tag: v2.6.15-rc1~59^2~15^2~175
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dacb16b1a034fa7a0b868ee30758119fbfd90bc1;p=pandora-kernel.git

[PATCH] i386 and x86_64 TSC set_cyc2ns_scale imprecision

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.

Fix the x86_64 architecture too.

Cc: george anzinger <george@mvista.com>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

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