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Message-ID: <20231102161949.IdSqSK2E@linutronix.de> Date: Thu, 2 Nov 2023 17:19:49 +0100 From: Sebastian Andrzej Siewior <bigeasy@...utronix.de> To: Peter Zijlstra <peterz@...radead.org> Cc: Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org, Daniel Bristot de Oliveira <bristot@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>, Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Vincent Guittot <vincent.guittot@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Tomas Glozar <tglozar@...hat.com> Subject: Re: [PATCH] sched/fair: Make the BW replenish timer expire in hardirq context for PREEMPT_RT On 2023-10-31 17:01:20 [+0100], Peter Zijlstra wrote: > On Mon, Oct 30, 2023 at 03:51:04PM +0100, Valentin Schneider wrote: > > task would get PI'd to FIFO1 (ktimers' default priority). Unfortunately, > > rwlocks cannot sanely do PI as they allow multiple readers. … > I'm thinking working on that is saner than adding this O(n) cgroup loop > to hard-irq context. Hmm? I have plans to get rid of the softirq issue and the argument for "bad" or inefficient rwlocks is usually "get rid of rwlocks then". So… Then I looked at the patch and it only swapped the flag nothing else and this hardly works. So I looked at sched_cfs_period_timer(): | static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) | { … | raw_spin_lock_irqsave(&cfs_b->lock, flags); … | raw_spin_unlock_irqrestore(&cfs_b->lock, flags); | | return idle ? HRTIMER_NORESTART : HRTIMER_RESTART; |} Judging by this, the whole callback runs already with disabled interrupts. At least now it enabled interrupts if multiple callbacks are invoked… Sebastian
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