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

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Message-Id: <20141209.143909.1690366723140906216.davem@davemloft.net>
Date:	Tue, 09 Dec 2014 14:39:09 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	netdev@...r.kernel.org, herbert@...dor.apana.org.au,
	jay.vosburgh@...onical.com, tgraf@...g.ch, dborkman@...hat.com,
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next] arch_fast_hash: avoid indirect function calls
 and implement hash in asm

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Thu,  4 Dec 2014 14:08:50 +0100

> 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.
> 
> To keep the number of clobbered registers short the hashing primitives
> are implemented in assembler. This makes it easier to do the dispatch
> by alternative_call.
> 
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: Jay Vosburgh <jay.vosburgh@...onical.com>
> Cc: Thomas Graf <tgraf@...g.ch>
> Cc: Daniel Borkmann <dborkman@...hat.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

I'm not applying this, I want this whole facility removed instead.
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