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From: John Baldwin <jhb@freebsd.org>
To: "Attilio Rao" <attilio@freebsd.org>
Date: Fri, 18 Jan 2008 09:29:44 -0500
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Cc: cvs-src@freebsd.org, src-committers@freebsd.org,
	David Xu <davidxu@freebsd.org>, cvs-all@freebsd.org
Subject: Re: cvs commit: src/sys/kern kern_time.c
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On Friday 18 January 2008 08:34:57 am Attilio Rao wrote:
> 2008/1/18, David Xu <davidxu@freebsd.org>:
> > davidxu     2008-01-18 13:00:28 UTC
> >
> >   FreeBSD src repository
> >
> >   Modified files:
> >     sys/kern             kern_time.c
> >   Log:
> >   Make sure reading td_runtime in critical section since thread may be
> >   preempted and td_runtime will be modified.
> 
> If you don't need the operation to be atomical with other operations
> inside the critical path (and I don't expect so) this change is
> pointless as our reading are always atomic.

Not on 32-bit archs like i386.  They may do two 32-bit reads and you could
have problems if the lower 32 wraps in between the reads.

-- 
John Baldwin