linux-kernel - Re: Using sched_clock for mmio-trace

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Message-Id: <1171725598.30834.125.camel@localhost.localdomain>
Date:	Sat, 17 Feb 2007 16:19:58 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>,
	Jeff Muizelaar <jeff@...idigm.net>,
	linux-kernel@...r.kernel.org
Subject: Re: Using sched_clock for mmio-trace

On Sat, 2007-02-17 at 15:56 +0100, Andi Kleen wrote:
> > This is one of the reasons why we don't just use good old
> > do_gettimeofday(), since it takes locks and can lead to lock recursion
> > if parts of itself are probed.
> 
> do_gettimeofday doesn't take locks.
> 
> Only restriction is that you can't single step it with long 
> pauses between instructions.

Err, it uses read side of xtime lock, so you can not call it from a
place which write locks xtime lock.

	tglx


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