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

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Message-ID: <CANn89i+XZtjD1RVBiFxfmsqZPMtN0156XgjUOkoOf8ohc7n+RQ@mail.gmail.com>
Date: Fri, 5 Apr 2024 10:46:28 +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 1:38 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