> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] > Sent: Thursday, January 7, 2016 8:28 AM > To: Simon Xiao <sixiao@xxxxxxxxxxxxx>; Eric Dumazet > <eric.dumazet@xxxxxxxxx> > Cc: Tom Herbert <tom@xxxxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx; KY > Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; > devel@xxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; David Miller > <davem@xxxxxxxxxxxxx> > Subject: Re: [PATCH net-next] hv_netvsc: don't make assumptions on > struct flow_keys layout > > Eric Dumazet <eric.dumazet@xxxxxxxxx> writes: > > > On Thu, 2016-01-07 at 10:33 +0100, Vitaly Kuznetsov wrote: > >> Recent changes to 'struct flow_keys' (e.g commit d34af823ff40 ("net: > Add > >> VLAN ID to flow_keys")) introduced a performance regression in > netvsc > >> driver. Is problem is, however, not the above mentioned commit but > the > >> fact that netvsc_set_hash() function did some assumptions on the > struct > >> flow_keys data layout and this is wrong. We need to extract the data > we > >> need (src/dst addresses and ports) after the dissect. > >> > >> The issue could also be solved in a completely different way: as > suggested > >> by Eric instead of our own homegrown netvsc_set_hash() we could use > >> skb_get_hash() which does more or less the same. Unfortunately, the > >> testing done by Simon showed that Hyper-V hosts are not happy with > our > >> Jenkins hash, selecting the output queue with the current algorithm > based > >> on Toeplitz hash works significantly better. > > > > Were tests done on IPv6 traffic ? > > > > Simon, could you please test this patch for IPv6 and show us the numbers? > > > Toeplitz hash takes at least 100 ns to hash 12 bytes (one iteration > per > > bit : 96 iterations) > > > > For IPv6 it is 3 times this, since we have to hash 36 bytes. > > > > I do not see how it can compete with skb_get_hash() that directly > gives > > skb->hash for local TCP flows. > > > > My guess is that this is not the bottleneck, something is happening > behind the scene with out packets in Hyper-V host (e.g. re-distributing > them to hardware queues?) but I don't know the internals, Microsoft > folks could probably comment. The Hyper-V vRSS protocol lets us use the Toeplitz hash algorithm. We are currently running further tests, including IPv6 too, and will share the results when available. Thanks, - Haiyang _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
