netdev - Re: [PATCH RESEND net-next v3] net: cache for same cpu skb_attempt_defer

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Message-ID: <CANn89iKZ4_ENsdOsMECd_7Np5imhqkJGatNXfrwMrgcgrLaUjg@mail.gmail.com>
Date: Fri, 5 Apr 2024 14:18:09 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, dsahern@...nel.org, 
	pabeni@...hat.com, kuba@...nel.org
Subject: Re: [PATCH RESEND net-next v3] net: cache for same cpu skb_attempt_defer_free

On Fri, Apr 5, 2024 at 1:55 PM Pavel Begunkov <asml.silence@...il.com> wrote:
>
> On 4/5/24 09:46, Eric Dumazet wrote:
> > On Fri, Apr 5, 2024 at 1:38 AM Pavel Begunkov <asml.silence@...il.com> wrote:
> >>
> >> Optimise skb_attempt_defer_free() when run by the same CPU the skb was
> >> allocated on. Instead of __kfree_skb() -> kmem_cache_free() we can
> >> disable softirqs and put the buffer into cpu local caches.
> >>
> >> CPU bound TCP ping pong style benchmarking (i.e. netbench) showed a 1%
> >> throughput increase (392.2 -> 396.4 Krps). Cross checking with profiles,
> >> the total CPU share of skb_attempt_defer_free() dropped by 0.6%. Note,
> >> I'd expect the win doubled with rx only benchmarks, as the optimisation
> >> is for the receive path, but the test spends >55% of CPU doing writes.
> >>
> >> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> >> ---
> >>
> >> v3: rebased, no changes otherwise
> >>
> >> v2: pass @napi_safe=true by using __napi_kfree_skb()
> >>
> >>   net/core/skbuff.c | 15 ++++++++++++++-
> >>   1 file changed, 14 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> >> index 2a5ce6667bbb..c4d36e462a9a 100644
> >> --- a/net/core/skbuff.c
> >> +++ b/net/core/skbuff.c
> >> @@ -6968,6 +6968,19 @@ void __skb_ext_put(struct skb_ext *ext)
> >>   EXPORT_SYMBOL(__skb_ext_put);
> >>   #endif /* CONFIG_SKB_EXTENSIONS */
> >>
> >> +static void kfree_skb_napi_cache(struct sk_buff *skb)
> >> +{
> >> +       /* if SKB is a clone, don't handle this case */
> >> +       if (skb->fclone != SKB_FCLONE_UNAVAILABLE) {
> >> +               __kfree_skb(skb);
> >> +               return;
> >> +       }
> >> +
> >> +       local_bh_disable();
> >> +       __napi_kfree_skb(skb, SKB_DROP_REASON_NOT_SPECIFIED);
> >
> > This needs to be SKB_CONSUMED
>
> Net folks and yourself were previously strictly insisting that
> every patch should do only one thing at a time without introducing
> unrelated changes. Considering it replaces __kfree_skb, which
> passes SKB_DROP_REASON_NOT_SPECIFIED, that should rather be a
> separate patch.

OK, I will send a patch myself.

__kfree_skb(skb) had no drop reason yet.

Here you are explicitly adding one wrong reason, this is why I gave feedback.