From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     jstultz@google.com, edumazet@google.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] softirq: don't yield if only expedited handlers are
 pending
In-Reply-To: <Y7viEa4BC3yJRXIS@hirez.programming.kicks-ass.net>
References: <20221222221244.1290833-1-kuba@kernel.org>
 <20221222221244.1290833-4-kuba@kernel.org>
 <Y7viEa4BC3yJRXIS@hirez.programming.kicks-ass.net>
Date:   Fri, 03 Mar 2023 12:41:27 +0100
Message-ID: <87sfemjc48.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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