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Groups > linux.kernel > #1303587
| From | Vitaly Kuznetsov <vkuznets@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout |
| Date | 2016-01-07 14:30 +0100 |
| Message-ID | <qOiNA-eq-7@gated-at.bofh.it> (permalink) |
| References | <qOfd0-6ef-15@gated-at.bofh.it> <qOiky-8ew-15@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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Eric Dumazet <eric.dumazet@gmail.com> 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.
> See commits b73c3d0e4f0e1961e15bec18720e48aabebe2109
> ("net: Save TX flow hash in sock and set in skbuf on xmit")
> and 877d1f6291f8e391237e324be58479a3e3a7407c
> ("net: Set sk_txhash from a random number")
>
> I understand Microsoft loves Toeplitz, but this looks not well placed
> here.
>
> I suspect there is another problem.
>
> Please share your numbers and test methodology, and the alternative
> patch Simon tested so that we can double check it.
>
Alternative patch which uses skb_get_hash() attached. Simon, could you
please share the rest (environment, metodology, numbers) with us here?
Thanks!
> Thanks.
>
> PS: For the time being this patch can probably be applied on -net tree,
> as it fixes a real bug.
--
Vitaly
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[PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-01-07 10:40 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Eric Dumazet <eric.dumazet@gmail.com> - 2016-01-07 14:00 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-01-07 14:30 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout John Fastabend <john.fastabend@gmail.com> - 2016-01-08 02:10 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout KY Srinivasan <kys@microsoft.com> - 2016-01-08 04:50 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout John Fastabend <john.fastabend@gmail.com> - 2016-01-08 07:20 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout KY Srinivasan <kys@microsoft.com> - 2016-01-08 19:10 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Haiyang Zhang <haiyangz@microsoft.com> - 2016-01-08 22:10 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Tom Herbert <tom@herbertland.com> - 2016-01-09 01:20 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout David Miller <davem@davemloft.net> - 2016-01-10 23:30 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Haiyang Zhang <haiyangz@microsoft.com> - 2016-01-14 00:30 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout David Miller <davem@davemloft.net> - 2016-01-14 06:00 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Tom Herbert <tom@herbertland.com> - 2016-01-14 18:20 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-01-14 19:00 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Eric Dumazet <eric.dumazet@gmail.com> - 2016-01-14 19:30 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Haiyang Zhang <haiyangz@microsoft.com> - 2016-01-14 19:40 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Tom Herbert <tom@herbertland.com> - 2016-01-14 19:50 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Haiyang Zhang <haiyangz@microsoft.com> - 2016-01-14 20:20 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Tom Herbert <tom@herbertland.com> - 2016-01-14 20:50 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Haiyang Zhang <haiyangz@microsoft.com> - 2016-01-14 21:30 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Tom Herbert <tom@herbertland.com> - 2016-01-14 22:50 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout David Miller <davem@davemloft.net> - 2016-01-14 23:10 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Eric Dumazet <eric.dumazet@gmail.com> - 2016-01-14 23:10 +0100
RE: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Haiyang Zhang <haiyangz@microsoft.com> - 2016-01-14 23:50 +0100
Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Eric Dumazet <eric.dumazet@gmail.com> - 2016-01-14 19:00 +0100
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