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Date: Tue, 20 Jul 2004 09:32:08 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
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To: Scott Long <scottl@samsco.org>
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cc: jesk <jesk@killall.org>
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Subject: Re: I/O or Threading Suffer
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On Tue, 20 Jul 2004, Scott Long wrote:

> If you are dd'ing from /dev/random, then you are depleting the entropy
> pool.  Anything else that tries to get random numbers is going to block
> in strange ways.  Trying just dd'ing from /dev/zero and see if that
> makes a difference. 

With Yarrow, /dev/random should just keep on chugging, so this is unlikely
to be the source.  However, lots of /dev/random I/O may take a while to
yield if it's working hard in kernel, so if that is combined with a
scheduling nit of some sort, we could be looking at a starvation issue.

Do we know if this is on a UP box or SMP box, and if so, whether it's
using HTT?  I could try reproducing it here and see if I see the same
thing.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research