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From: Thomas Gleixner <tglx@linutronix.de>
To: peterz@infradead.org
Cc: mw@semihalf.com, paulmck@kernel.org,
	Anna-Maria Gleixner <anna-maria@linutronix.de>,
	catalin.marinas@arm.com, Alison Wang <alison.wang@nxp.com>,
	linux-kernel@vger.kernel.org, leoyang.li@nxp.com,
	vladimir.oltean@nxp.com,
	Kurt Kanzenbach <kurt.kanzenbach@linutronix.de>,
	Vladimir Oltean <olteanv@gmail.com>,
	will@kernel.org, Valentin Schneider <valentin.schneider@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting
Date: Thu, 06 Aug 2020 20:58:26 +0200	[thread overview]
Message-ID: <87mu37ha99.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200806114545.GA2674@hirez.programming.kicks-ass.net>

Peter,

peterz@infradead.org writes:
> On Thu, Aug 06, 2020 at 11:41:06AM +0200, Thomas Gleixner wrote:
>> And that has nothing to do
>> with a silly test case. Sporadic runaways due to a bug in a once per
>> week code path simply can happen and having the safety net working
>> depending on a config option selected or not is just wrong.
>
> The safety thing is concerned with RT tasks. It doesn't pretend to help
> with runnaway IRQs, never has, never will.

Of course not. But without irq accounting the runtime is accounted on
the runaway task which causes it to throttle.

> The further extreme is an interrupt storm, those have always taken a
> machine down.

If every interrupt is actually handled, then yes.

> Accounting unrelated IRQ time to RT tasks is equally wrong, the task
> execution is unrelated to the IRQs. The config option at least offers
> insight into where time goes -- and it's a config option because doing
> time accounting on interrupts adds overhead :/

Right, but it's not totally out of the world either to make the
throttler do:

          if (rt_runtime + irq_time > threshold)
          	try_to_keep_the_box_alive()

> This really is a no-win all round.

That's not the question here :)

> The only 'sensible' option here is threaded IRQs, where the IRQ line
> gets disabled until the handler thread has ran, that also helps with IRQ
> storms.

I'm not against enforcing threaded IRQs. :)

Thanks,

        tglx

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  parent reply	other threads:[~2020-08-06 18:59 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-29  3:39 [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting Alison Wang
2020-07-29  8:40 ` Kurt Kanzenbach
2020-07-29  8:50   ` [EXT] " Alison Wang
2020-07-29  9:49   ` Vladimir Oltean
2020-07-30  7:23     ` Kurt Kanzenbach
2020-07-30  8:22       ` Vladimir Oltean
2020-08-03  8:04         ` Kurt Kanzenbach
2020-08-03  8:16           ` Vladimir Oltean
2020-08-03  9:51             ` Robin Murphy
2020-08-03 11:38               ` Vladimir Oltean
2020-08-03 11:48                 ` Valentin Schneider
2020-08-03 13:24                   ` Marc Zyngier
2020-08-03 10:02             ` Thomas Gleixner
2020-08-03 10:49           ` Thomas Gleixner
2020-08-03 11:41             ` Vladimir Oltean
2020-08-03 15:13               ` Thomas Gleixner
2020-08-03 15:47                 ` Valentin Schneider
2020-08-03 16:14                   ` Vladimir Oltean
2020-08-03 19:22                   ` Thomas Gleixner
2020-08-03 23:59                     ` Valentin Schneider
2020-08-05  8:50                       ` Dietmar Eggemann
2020-08-05 13:40                     ` peterz
2020-08-05 13:56                       ` Valentin Schneider
2020-08-05 15:31                         ` peterz
2020-08-06  9:41                           ` Thomas Gleixner
2020-08-06 11:45                             ` peterz
2020-08-06 13:27                               ` Paul E. McKenney
2020-08-06 19:03                                 ` Thomas Gleixner
2020-08-06 20:39                                   ` Paul E. McKenney
2020-08-06 18:58                               ` Thomas Gleixner [this message]
2020-08-06  9:34                       ` Thomas Gleixner

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