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From: Thomas Gleixner <tglx@linutronix.de>
To: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: linux-rt-users@vger.kernel.org, frederic@kernel.org,
	mtosatti@redhat.com, LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC 2/2] timers: Make sure irq_work is handled when no pending timers
Date: Sat, 19 Jun 2021 10:22:43 +0200	[thread overview]
Message-ID: <875yyae018.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <87mtrmeqon.ffs@nanos.tec.linutronix.de>

On Sat, Jun 19 2021 at 00:47, Thomas Gleixner wrote:
> On Thu, Jun 10 2021 at 14:59, Nicolas Saenz Julienne wrote:
> As we since then made work queues RT aware and it's possible to queue
> work from the irq_work IPI context, the obvious solution is to delegate
> this to a work queue.
>
> If we do a proper analysis of the affected irq work callbacks then this
> probably makes a lot of sense independent of RT. There are only a few
> really urgent irq work items which need to be handled immediately in the
> IPI.
>
> RT is special, but as we have demonstrated over time it's not _that_
> special. It just needs a proper analysis and a real good argument why
> something has to be special for RT and does not fit into the common
> case. Or to demonstrate that the common case approach of 'do it right
> away' is pointless or even harmfull.

I skimmed most of the ~40 irq_work instances.

Most of them have no urgency at all. And out of those non-urgent cases
the majority does not even have the requirement to run on the current
CPU, so they can be pushed off to a global work queue which moves them
away from NOHZ full CPUs completely.

That has nothing to do with RT, that's a benefit in general.

Thanks,

        tglx


  reply	other threads:[~2021-06-19  8:23 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210610125945.558872-1-nsaenzju@redhat.com>
2021-06-18 21:06 ` [RFC 1/2] timers: Add pending timer bool in struct timer_base Thomas Gleixner
     [not found] ` <20210610125945.558872-2-nsaenzju@redhat.com>
2021-06-18 22:47   ` [RFC 2/2] timers: Make sure irq_work is handled when no pending timers Thomas Gleixner
2021-06-19  8:22     ` Thomas Gleixner [this message]
2021-06-22 13:44     ` Peter Zijlstra
2021-06-22 17:33       ` Jiri Olsa
2021-06-22 17:42         ` Jiri Olsa

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