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From: Andi Kleen <andi@firstfloor.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <andi@firstfloor.org>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Jeff Muizelaar <jeff@infidigm.net>,
	linux-kernel@vger.kernel.org
Subject: Re: Using sched_clock for mmio-trace
Date: Sun, 18 Feb 2007 18:20:43 +0100	[thread overview]
Message-ID: <20070218172043.GA7340@one.firstfloor.org> (raw)
In-Reply-To: <1171725598.30834.125.camel@localhost.localdomain>

On Sat, Feb 17, 2007 at 04:19:58PM +0100, Thomas Gleixner wrote:
> 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.

Err, you can -- seqlocks never deadlock.

The only thing that doesn't work is to single step with long enough
pauses with interrupts on inbetween that the sequence numbers increase:
you get a livelock then.

-Andi

  reply	other threads:[~2007-02-18 17:20 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-16  1:30 Using sched_clock for mmio-trace Jeff Muizelaar
2007-02-16 16:30 ` Frank Ch. Eigler
2007-02-16 17:45   ` Daniel Walker
2007-02-16 18:10     ` Jeff Muizelaar
2007-02-16 18:28       ` Daniel Walker
2007-02-16 19:34         ` Jeff Muizelaar
2007-02-16 21:06           ` Daniel Walker
2007-02-16 22:10             ` Jeff Muizelaar
2007-02-16 22:47               ` Daniel Walker
2007-02-17  4:36                 ` Jeff Muizelaar
2007-02-16 18:30   ` Jeff Muizelaar
2007-02-16 18:44     ` Randy Dunlap
2007-02-16 19:55       ` Jeff Muizelaar
2007-02-16 20:03   ` Andi Kleen
2007-02-16 21:26     ` Frank Ch. Eigler
2007-02-17 14:56       ` Andi Kleen
2007-02-17 15:19         ` Thomas Gleixner
2007-02-18 17:20           ` Andi Kleen [this message]
2007-02-16 20:02 ` Andi Kleen
2007-02-16 19:40   ` Jeff Muizelaar

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