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From: Philipp Kohlbecher <xt28@gmx.de>
To: linux-kernel@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>, John Stultz <johnstul@us.ibm.com>
Subject: clocksources: order of preference
Date: Thu, 08 May 2008 12:40:54 +0200	[thread overview]
Message-ID: <4822D8B6.4090008@gmx.de> (raw)

Why is the TSC preferred to the HPET as a clocksource for the x86 
architecture?

"Understanding the Linux Kernel" states that the HPET is preferable to 
the TSC due to its richer architecture. Up to version 2.6.17.14, 
arch/i386/kernel/timers/timer.c also contained a comment to that effect 
and accordingly ranked the HPET before the TSC.

This was changed when the new clocksource infrastructure was introduced 
with version 2.6.18. (The HPET clocksource received a rating of 250; the 
TSC, 300.)

Preferring the TSC leads to problems when it is unstable. While this can 
be prevented by setting CONFIG_X86_TSC, certain distribution kernels 
(striving for compatibility) don't, resulting in soft lockups.

Are there better reasons to prefer the TSC or may I submit a patch that 
swaps the respective ratings?

Thanks for reading,
- Philipp Kohlbecher

Please CC me, I am not on the list.

             reply	other threads:[~2008-05-08 10:41 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-05-08 10:40 Philipp Kohlbecher [this message]
2008-05-08 10:59 ` clocksources: order of preference Thomas Gleixner
2008-05-08 11:07   ` Philipp Kohlbecher
2008-05-08 11:46     ` Thomas Gleixner

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