From: Greg Banks <gnb@sgi.com>
Subject: Re: [RFC,PATCH 4/14] knfsd: has_wspace per transport
Date: Thu, 24 May 2007 00:39:03 +1000
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Cc: "Talpey, Thomas" <Thomas.Talpey@netapp.com>,
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	"J. Bruce Fields" <bfields@fieldses.org>,
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To: Chuck Lever <chuck.lever@oracle.com>
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On Wed, May 23, 2007 at 09:36:55AM -0400, Chuck Lever wrote:
> Greg Banks wrote:
> >On Wed, May 23, 2007 at 12:22:44AM -0500, Tom Tucker wrote:
> >>
> >>
> >>On 5/22/07 9:32 PM, "Greg Banks" <gnb@sgi.com> wrote:
> >>
> >>>On Tue, May 22, 2007 at 12:34:23PM -0500, Tom Tucker wrote:
> >>I need to do a little clean up (e.g. atomic_inc()) and then I'll add them 
> >>as
> >>suggested. If there are dissenters, please speak now...
> >
> >You should be able to get away with just ++.  They're only stats,
> >it's not like you have logic depending on them being exact.
> 
> The usual way to do this is to allocate separate stat arrays for each 
> CPU.  All the per-CPU arrays are summed only when something wants to 
> display stat totals.
> 
> That way you can use ++, be fairly sure you will get accurate 
> statistics, and not have to be concerned about CPU cache effects or lock 
> contention.

Here in SGI, home of the multiple-thousand CPU Linux boxes, making
data structures per-cpu tends to be done...thoughtfully.

In any case, the remainder of svc_stat gets no such treatment today.

Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
Apparently, I'm Bedevere.  Which MPHG character are you?
I don't speak for SGI.

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