From: Greg Banks <gnb@sgi.com>
Subject: Re: [PATCH 7/8] knfsd: repcache: faster hash chain probe
Date: Mon, 16 Oct 2006 21:02:08 +1000
Message-ID: <20061016110208.GE8568@sgi.com>
References: <1160566178.8530.19.camel@hole.melbourne.sgi.com>
	<17714.61390.225292.840864@cse.unsw.edu.au>
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Cc: Linux NFS Mailing List <nfs@lists.sourceforge.net>
To: Neil Brown <neilb@suse.de>
In-Reply-To: <17714.61390.225292.840864@cse.unsw.edu.au>
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On Mon, Oct 16, 2006 at 12:34:54PM +1000, Neil Brown wrote:
> On Wednesday October 11, gnb@melbourne.sgi.com wrote:
> > knfsd: Squeeze some small performance improvements out of the duplicate
> > request cache's lookup function by reducing the number of instructions
> > to compare each entry during hash chain probing.
> > 
> > Comparisons such as the RPC protocol number and version which are going
> > to be the same for almost all entries are now done last.  Comparisons
> > such as xid and client IP address which are more likely to differ
> > between entries are done first.  The client IP address comparison
> > is fixed not to compare 8 bytes of zeroes and to do comparisons as
> > 32b quantities.  Finally, a 32b addition for the timestamp is removed
> > from the loop by taking advantage of a loop invariant.
> 
> And yet:
> 
> > +static inline int
> > +compare_sockaddr_in(const struct sockaddr_in *sina, const struct sockaddr_in *sinb)
> > +{
> > +	return ((*(u32 *)&sina->sin_family == *(u32 *)&sinb->sin_family) &&
> > +		(sina->sin_addr.s_addr == sinb->sin_addr.s_addr));
> > +}
> > +
> 
> You compare family and port before address.... I suspect you would
> find the port is the same between clients more often than the address.

Excellent point, I'll fix that.

> Is there a reason?

Not one that I'd want to defend ;-)

Greg.
-- 
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.

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