netdev - Re: [PATCH net-next] arch_fast_hash: avoid indirect function calls and implement hash in asm

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Message-ID: <1417711030.5386.35.camel@localhost>
Date:	Thu, 04 Dec 2014 17:37:10 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	netdev@...r.kernel.org, Jay Vosburgh <jay.vosburgh@...onical.com>,
	Thomas Graf <tgraf@...g.ch>,
	Daniel Borkmann <dborkman@...hat.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] arch_fast_hash: avoid indirect function calls
 and implement hash in asm

On Do, 2014-12-04 at 23:56 +0800, Herbert Xu wrote:
> On Thu, Dec 04, 2014 at 02:08:50PM +0100, Hannes Frederic Sowa wrote:
> > By default the arch_fast_hash hashing function pointers are initialized
> > to jhash(2). If during boot-up a CPU with SSE4.2 is detected they get
> > updated to the CRC32 ones. This dispatching scheme incurs a function
> > pointer lookup and indirect call for every hashing operation.
> 
> Just curious, is jhash actually faster than generic C CRC32 on
> common platforms?

Yes, jhash always beats crc32 in software on x86_64 and ia32.

Bye,
Hannes


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