netdev - Re: [PATCH net-next 2/3] net: skbuff: cache one skb

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Message-ID: <20230215095200.0d2e3b7e@kernel.org>
Date:   Wed, 15 Feb 2023 09:52:00 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Edward Cree <ecree.xilinx@...il.com>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>, <edumazet@...gle.com>,
        <pabeni@...hat.com>, <willemb@...gle.com>, <fw@...len.de>
Subject: Re: [PATCH net-next 2/3] net: skbuff: cache one skb_ext for use by
 GRO

On Wed, 15 Feb 2023 17:17:53 +0100 Alexander Lobakin wrote:
> > On 15/02/2023 03:43, Jakub Kicinski wrote:  
> >> On the driver -> GRO path we can avoid thrashing the kmemcache
> >> by holding onto one skb_ext.  
> > 
> > Hmm, will one be enough if we're doing GRO_NORMAL batching?
> > As for e.g. UDP traffic up to 8 skbs (by default) can have
> >  overlapping lifetimes.
> >   
> I thought of an array of %NAPI_SKB_CACHE_SIZE to be honest. From what
> I've ever tested, no cache (for any netstack-related object) is enough
> if it can't serve one full NAPI poll :D

I was hoping to leave sizing of the cache until we have some data from
a production network (or at least representative packet traces).

NAPI_SKB_CACHE_SIZE kinda assumes we're not doing much GRO, right?
And the current patch feeds the cache exclusively from GRO...

> + agree with Paolo re napi_reuse_skb(), it's used only in the NAPI
> context and recycles a lot o'stuff already, we can speed it up safely here.

LMK what's your opinion on touching the other potential spots, too.
(in Paolo's subthread).