* 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 ^ permalink raw reply [flat|nested] 2+ messages in thread
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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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