netdev - Re: [PATCH 3/3] softirq: don't yield if only expedited handlers are pending

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Date:   Fri, 03 Mar 2023 12:41:27 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     jstultz@...gle.com, edumazet@...gle.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] softirq: don't yield if only expedited handlers are
 pending

On Mon, Jan 09 2023 at 10:44, Peter Zijlstra wrote:
> On Thu, Dec 22, 2022 at 02:12:44PM -0800, Jakub Kicinski wrote:
>> Tweak the need_resched() condition to be ignored if all pending
>> softIRQs are "non-deferred". The tasklet would run relatively
>> soon, anyway, but once ksoftirqd is woken we're risking stalls.
>> 
>> I did not see any negative impact on the latency in an RR test
>> on a loaded machine with this change applied.
>
> Ignoring need_resched() will get you in trouble with RT people real
> fast.

In this case not really. softirq processing is preemptible in RT, but
it's still a major pain ...

Thanks,

        tglx