linux-kernel - Re: [PATCH net-next 1/3] net: netpoll: Defer skb

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Message-ID: <20241101190101.4a2b765f@kernel.org>
Date: Fri, 1 Nov 2024 19:01:01 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: horms@...nel.org, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, thepacketgeek@...il.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, davej@...emonkey.org.uk, vlad.wing@...il.com,
 max@...sevol.com, kernel-team@...a.com, jiri@...nulli.us, jv@...sburgh.net,
 andy@...yhouse.net, aehkn@...hub.one, Rik van Riel <riel@...riel.com>, Al
 Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH net-next 1/3] net: netpoll: Defer skb_pool population
 until setup success

On Fri, 1 Nov 2024 11:18:29 -0700 Breno Leitao wrote:
> > I think that a best mechanism might be something like:
> > 
> >  * If find_skb() needs to consume from the pool (which is rare, only
> > when alloc_skb() fails), raise workthread that tries to repopulate the
> > pool in the background. 
> > 
> >  * Eventually avoid alloc_skb() first, and getting directly from the
> >    pool first, if the pool is depleted, try to alloc_skb(GPF_ATOMIC).
> >    This might make the code faster, but, I don't have data yet.  
> 
> I've hacked this case (getting the skb from the pool first and refilling
> it on a workqueue) today, and the performance is expressive.
> 
> I've tested sending 2k messages, and meassured the time it takes to
> run `netpoll_send_udp`, which is the critical function in netpoll.

The purpose of the pool is to have a reserve in case of OOM, AFAIU.
We may speed things up by taking the allocations out of line but
we risk the pool being empty when we really need it.