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Date: Fri, 29 Jan 2010 16:45:01 +0530 From: Krishna Kumar2 <krkumar2@...ibm.com> To: Herbert Xu <herbert@...dor.apana.org.au> Cc: David Miller <davem@...emloft.net>, eric.dumazet@...il.com, ilpo.jarvinen@...sinki.fi, netdev@...r.kernel.org Subject: Re: [RFC] [PATCH] Optimize TCP sendmsg in favour of fast devices? > Herbert Xu <herbert@...dor.apana.org.au> wrote on 01/29/2010 02:36:25 PM: > > > I ran 5 serial netperf's with 16K and another 5 serial netperfs > > with 64K I/O sizes, and the aggregate result is: > > > > 0. Driver unsets F_SG but sets F_GSO: > > Original code with 16K: 19471.65 > > New code with 16K: 19409.70 > > Original code with 64K: 21357.23 > > New code with 64K: 22050.42 > > OK this is more in line with what I was expecting, namely that > enabling GSO is actually beneficial even without SG. > > It would be good to get the CPU utilisation figures so we can > see the complete picture. Same 5 runs of single netperf's: 0. Driver unsets F_SG but sets F_GSO: Org (16K): BW: 18180.71 SD: 13.485 New (16K): BW: 18113.15 SD: 13.551 Org (64K): BW: 21980.28 SD: 10.306 New (64K): BW: 21386.59 SD: 10.447 1. Driver unsets F_SG, and with GSO off Org (16K): BW: 10894.62 SD: 26.591 New (16K): BW: 7262.10 SD: 35.340 Org (64K): BW: 12396.41 SD: 23.357 New (64K): BW: 7853.02 SD: 32.405 2. Driver unsets F_SG and uses ethtool to set GSO: Org (16K): BW: 18094.11 SD: 13.603 New (16K): BW: 17952.38 SD: 13.743 Org (64K): BW: 21540.78 SD: 10.771 New (64K): BW: 21818.35 SD: 10.598 > > I should have mentioned this too - if I unset F_SG in the > > cxgb3 driver and nothing else, ethtool -k still shows GSO > > is set, and tcpdump shows max packet size is 1448. If I > > additionally set GSO in driver, then ethtool still has the > > same output, but tcpdump shows max packet size of 65160. > > This sounds like a bug. Yes, an ethtool bug (version 6). The test case #1 above, I have written that GSO is off but ethtool "thinks" it is on (after a modprobe -r cxgb3; modprobe cxgb3). So for test #2, I simply run "ethtool ... gso on", and GSO is now really on in the kernel, explaining the better results. thanks, - KK -- 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
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