linux-kernel - Re: [PATCH] x86: set_cyc2ns_scale() remove tsc_now and ns

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Message-ID: <873apsn8g7.fsf@basil.nowhere.org>
Date:	Fri, 11 Apr 2008 09:42:48 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Karsten Wiese <fzu@...gehoertderstaat.de>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] x86: set_cyc2ns_scale() remove tsc_now and ns_now

Karsten Wiese <fzu@...gehoertderstaat.de> writes:

> Both are unused and the functions rdtscll() and __cycles_2_ns() don't have
> side-effects.

I don't think you should remove those. At some point the offset
needs to be reset when the frequency scale changes for obvious reasons, 
and that needs to be fixed, not the code removed. Right now you'll get
scheduling inconsistencies during frequency changes on 
!constant_tsc CPUs.

(actually it is still the wrong time -- really needs a grace 
period during which the TSC is not used
ftp://firstfloor.org/pub/ak/quilt/patches/sched-clock implemented
some of these ideas against an older kernel)

-Andi

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