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

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Message-ID: <30882f03-0094-42c7-b459-3f240ae94f20@gmail.com>
Date: Fri, 5 Apr 2024 13:35:44 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Eric Dumazet <edumazet@...gle.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 4/5/24 13:18, Eric Dumazet wrote:
> 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.

Ok, alternatively, I can make it a series adding it on top.


> __kfree_skb(skb) had no drop reason yet.
> 
> Here you are explicitly adding one wrong reason, this is why I gave feedback.

-- 
Pavel Begunkov