lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Sun, 28 Sep 2014 17:43:41 -0400 (EDT) From: David Miller <davem@...emloft.net> To: eric.dumazet@...il.com Cc: therbert@...gle.com, brouer@...hat.com, netdev@...r.kernel.org, alexander.h.duyck@...el.com, toke@...e.dk, fw@...len.de, jhs@...atatu.com, dave.taht@...il.com, john.r.fastabend@...el.com, dborkman@...hat.com, hannes@...essinduktion.org Subject: Re: [PATCH net-next] dql: dql_queued() should write first to reduce bus transactions From: Eric Dumazet <eric.dumazet@...il.com> Date: Thu, 25 Sep 2014 23:04:56 -0700 > From: Eric Dumazet <edumazet@...gle.com> > > While doing high throughput test on a BQL enabled NIC, > I found a very high cost in ndo_start_xmit() when accessing BQL data. > > It turned out the problem was caused by compiler trying to be > smart, but involving a bad MESI transaction : > > 0.05 │ mov 0xc0(%rax),%edi // LOAD dql->num_queued > 0.48 │ mov %edx,0xc8(%rax) // STORE dql->last_obj_cnt = count > 58.23 │ add %edx,%edi > 0.58 │ cmp %edi,0xc4(%rax) > 0.76 │ mov %edi,0xc0(%rax) // STORE dql->num_queued += count > 0.72 │ js bd8 > > > I got an incredible 10 % gain [1] by making sure cpu do not attempt > to get the cache line in Shared mode, but directly requests for > ownership. > > New code : > mov %edx,0xc8(%rax) // STORE dql->last_obj_cnt = count > add %edx,0xc0(%rax) // RMW dql->num_queued += count > mov 0xc4(%rax),%ecx // LOAD dql->adj_limit > mov 0xc0(%rax),%edx // LOAD dql->num_queued > cmp %edx,%ecx > > The TX completion was running from another cpu, with high interrupts > rate. > > Note that I am using barrier() as a soft hint, as mb() here could be > too heavy cost. > > [1] This was a netperf TCP_STREAM with TSO disabled, but GSO enabled. > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> Ok now you're just showing off :-) Applied, thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists