linux-kernel - Re: CONFIG_NO_HZ breaks blktrace timestamps

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Message-ID: <20080111094205.GE8143@elte.hu>
Date:	Fri, 11 Jan 2008 10:42:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	David Dillow <dillowda@...l.gov>,
	Guillaume Chazarain <guichaz@...oo.fr>,
	linux-kernel@...r.kernel.org, linux-btrace@...r.kernel.org,
	mingo@...hat.com, tglx@...utronix.de
Subject: Re: CONFIG_NO_HZ breaks blktrace timestamps


* Jens Axboe <jens.axboe@...cle.com> wrote:

> > they are from the scheduler git tree (except the first debug patch), 
> > but queued up for v2.6.25 at the moment.
> 
> So this means that blktrace will be broken with CONFIG_NO_HZ for 
> 2.6.24? That's clearly a regression.

64-bit CONFIG_NO_HZ is a new feature in v2.6.24. If it happens on 32-bit 
too and it didnt happen in v2.6.23 32-bit then it's a regression.

all this comes from blktrace's original decision of using sched_clock()
:-) It's not a global timesource and it's not trivial to turn it into a
halfways usable global timesource.

	Ingo
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