linux-kernel - Re: [PATCH] Add an offset in the cyc2ns computation to fix sched

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Date:	Fri, 16 Mar 2007 19:36:18 +0100 (CET)
From:	Andreas Kleen <ak@...e.de>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Guillaume Chazarain <guichaz@...il.com>,
	john stultz <johnstul@...ibm.com>,
	mathieu.desnoyers@...ymtl.ca, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add an offset in the cyc2ns computation to fix	sched_clock jumps

Am Fr 16.03.2007 19:30 schrieb Daniel Walker <dwalker@...sta.com>:

> On Fri, 2007-03-16 at 19:14 +0100, Guillaume Chazarain wrote:
> > Hello,
> >
> > The scheduling problems I reported in the thread:
> > http://lkml.org/lkml/2007/3/3/128
> > are caused by the set_cyc2ns_scale() function called when the CPU
> > speed changes.
> > Changing the scale causes a warp in the value returned by
> > sched_clock().
> >
>
> Did you explain what the "werirdnes" was exactly? If not, could you?

I fixed this in my own version of the change by marking it unstable
during the transition
(concept stolen from Jiri's patch). Basically watch the notifiers for
before/after
and while the transition is in progress always ask for that underlying
monotonic ktime.

-Andi


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