linux-kernel - Re: [PATCH 0/3] softirq: uncontroversial change

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Date:   Thu, 20 Apr 2023 22:23:14 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, peterz@...radead.org,
        tglx@...utronix.de, jstultz@...gle.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] softirq: uncontroversial change

On Thu, 2023-04-20 at 19:41 +0200, Eric Dumazet wrote:
> On Thu, Apr 20, 2023 at 7:24 PM Paolo Abeni <pabeni@...hat.com> wrote:
> > I would like to propose a revert of:
> > 
> > 4cd13c21b207 softirq: Let ksoftirqd do its job
> > 
> > the its follow-ups:
> > 
> > 3c53776e29f8 Mark HI and TASKLET softirq synchronous
> > 0f50524789fc softirq: Don't skip softirq execution when softirq thread is parking
> > 
> > The problem originally addressed by 4cd13c21b207 can now be tackled
> > with the threaded napi, available since:
> > 
> > 29863d41bb6e net: implement threaded-able napi poll loop support
> > 
> > Reverting the mentioned commit should address the latency issues
> > mentioned by Jakub - I verified it solves a somewhat related problem in
> > my setup - and reduces the layering of heuristics in this area.
> > 
> > A refactor introducing uniform overload detection and proper resource
> > control will be better, but I admit it's beyond me and anyway it could
> > still land afterwards.
> > 
> > Any opinion more then welcome!
> 
> Seems fine, but I think few things need to be fixed first in
> napi_threaded_poll()
> to enable some important features that are currently  in net_rx_action() only.

Thanks for the feedback.

I fear I'll miss some relevant bits. 

On top of my head I think about RPS and  skb_defer_free. Both should
work even when napi threaded is enabled - with an additional softirq ;)
Do you think we should be able to handle both inside the napi thread?
Or do you refer to other features?

Thanks!

Paolo