* Re: [PATCH net-next] arch_fast_hash: avoid indirect function calls and implement hash in asm
[not found] <e77237174e1b8d743ef5171e05abde82bc54af37.1417696901.git.hannes@stressinduktion.org>
@ 2014-12-04 15:56 ` Herbert Xu
2014-12-04 16:37 ` Hannes Frederic Sowa
0 siblings, 1 reply; 2+ messages in thread
From: Herbert Xu @ 2014-12-04 15:56 UTC (permalink / raw)
To: Hannes Frederic Sowa
Cc: netdev, Jay Vosburgh, Thomas Graf, Daniel Borkmann, Eric Dumazet,
Linux Kernel Mailing List
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?
Cheers,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH net-next] arch_fast_hash: avoid indirect function calls and implement hash in asm
2014-12-04 15:56 ` [PATCH net-next] arch_fast_hash: avoid indirect function calls and implement hash in asm Herbert Xu
@ 2014-12-04 16:37 ` Hannes Frederic Sowa
0 siblings, 0 replies; 2+ messages in thread
From: Hannes Frederic Sowa @ 2014-12-04 16:37 UTC (permalink / raw)
To: Herbert Xu
Cc: netdev, Jay Vosburgh, Thomas Graf, Daniel Borkmann, Eric Dumazet,
Linux Kernel Mailing List
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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2014-12-04 15:56 ` [PATCH net-next] arch_fast_hash: avoid indirect function calls and implement hash in asm Herbert Xu
2014-12-04 16:37 ` Hannes Frederic Sowa
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