Messages in this thread | | | From | Eric Dumazet <> | Date | Tue, 12 Jan 2021 20:19:14 +0100 | Subject | Re: [PATCH net-next 0/5] skbuff: introduce skbuff_heads bulking and reusing |
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On Tue, Jan 12, 2021 at 7:26 PM Alexander Lobakin <alobakin@pm.me> wrote: > > From: Eric Dumazet <edumazet@google.com> > Date: Tue, 12 Jan 2021 13:32:56 +0100 > > > On Tue, Jan 12, 2021 at 11:56 AM Alexander Lobakin <alobakin@pm.me> wrote: > >> > > > >> > >> Ah, I should've mentioned that I use UDP GRO Fraglists, so these > >> numbers are for GRO. > >> > > > > Right, this suggests UDP GRO fraglist is a pathological case of GRO, > > not saving memory. > > > > Real GRO (TCP in most cases) will consume one skb, and have page > > fragments for each segment. > > > > Having skbs linked together is not cache friendly. > > OK, so I rebased test setup a bit to clarify the things out. > > I disabled fraglists and GRO/GSO fraglists support advertisement > in driver to exclude any "pathological" cases and switched it > from napi_get_frags() + napi_gro_frags() to napi_alloc_skb() + > napi_gro_receive() to disable local skb reusing (napi_reuse_skb()). > I also enabled GSO UDP L4 ("classic" one: one skbuff_head + frags) > for forwarding, not only local traffic, and disabled NF flow offload > to increase CPU loading and drop performance below link speed so I > could see the changes. > > So, the traffic flows looked like: > - TCP GRO (one head + frags) -> NAT -> hardware TSO; > - UDP GRO (one head + frags) -> NAT -> driver-side GSO. > > Baseline 5.11-rc3: > - 865 Mbps TCP, 866 Mbps UDP. > > This patch (both separate caches and Edward's unified cache): > - 899 Mbps TCP, 893 Mbps UDP. > > So that's cleary *not* only "pathological" UDP GRO Fraglists > "problem" as TCP also got ~35 Mbps from this, as well as > non-fraglisted UDP. > > Regarding latencies: I remember there were talks about latencies when > Edward introduced batched GRO (using linked lists to pass skbs from > GRO layer to core stack instead of passing one by one), so I think > it's a perennial question when it comes to batching/caching. > > Thanks for the feedback, will post v2 soon. > The question about if this caching is reasonable isn't closed anyway, > but I don't see significant "cons" for now. >
Also it would be nice to have KASAN support.
We do not want to unconditionally to recycle stuff, since this might hide use-after-free.
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