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From: Grant Likely <grant.likely@secretlab.ca>
Date: Tue, 26 May 2009 22:00:51 -0600
Message-ID: <fa686aa40905262100v64a01d41q65ff39ad953305a3@mail.gmail.com>
Subject: Re: [alsa-devel] [PATCH] Modify mpc5200 AC97 driver to use V9 of
	spin_event_timeout()
To: Jon Smirl <jonsmirl@gmail.com>
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Cc: linuxppc-dev@ozlabs.org, alsa-devel@alsa-project.org,
	Timur Tabi <timur@freescale.com>, broonie@sirena.org.uk
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On Tue, May 26, 2009 at 9:48 PM, Grant Likely <grant.likely@secretlab.ca> w=
rote:
> First, udelay just burns time, and if the delay is too large, then the
> it is wasting time that could be used for something else. =A0That being
> said, it needs to be balanced with the context switch overhead. =A0If
> the udelay() is less than double the context switch time, then the
> overhead is greater than the time spent spinning.

BTW, lmbench lat_ctx test case tells me that context switch latency is
measured somewhere around 30 to 60 us for user space processes
sleeping on a file descriptor.  That will be lower for kernel threads
since there is no syscall overhead to account for.

g.

--=20
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.