From: Neil Brown <neilb@suse.de>
Subject: Re: [PATCH 7/8] knfsd: repcache: faster hash chain probe
Date: Mon, 16 Oct 2006 12:34:54 +1000
Message-ID: <17714.61390.225292.840864@cse.unsw.edu.au>
References: <1160566178.8530.19.camel@hole.melbourne.sgi.com>
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Cc: Linux NFS Mailing List <nfs@lists.sourceforge.net>
To: Greg Banks <gnb@melbourne.sgi.com>
In-Reply-To: message from Greg Banks on Wednesday October 11
Sender: nfs-bounces@lists.sourceforge.net
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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.

Is there a reason?

NeilBrown

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