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From: Valentin Schneider <valentin.schneider@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>
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,
	Peter Zijlstra <peterz@infradead.org>,
	vladimir.oltean@nxp.com,
	Kurt Kanzenbach <kurt.kanzenbach@linutronix.de>,
	Vladimir Oltean <olteanv@gmail.com>,
	will@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting
Date: Mon, 03 Aug 2020 16:47:03 +0100	[thread overview]
Message-ID: <jhjh7tjivew.mognet@arm.com> (raw)
In-Reply-To: <87d047n4oh.fsf@nanos.tec.linutronix.de>


On 03/08/20 16:13, Thomas Gleixner wrote:
> Vladimir Oltean <olteanv@gmail.com> writes:
>>>  1) When irq accounting is disabled, RT throttling kicks in as
>>>     expected.
>>> 
>>>  2) With irq accounting the RT throttler does not kick in and the RCU
>>>     stall/lockups happen.
>> What is this telling us?
>
> It seems that the fine grained irq time accounting affects the runtime
> accounting in some way which I haven't figured out yet.
>

With IRQ_TIME_ACCOUNTING, rq_clock_task() will always be incremented by a
lesser-or-equal value than when not having the option; you start with the
same delta_exec but slice some for the IRQ accounting, and leave the rest
for the rq_clock_task() (+paravirt).

IIUC this means that if you spend e.g. 10% of the time in IRQ and 90% of
the time running the stress-ng RT tasks, despite having RT tasks hogging
the entirety of the "available time" it is still only 90% runtime, which is
below the 95% default and the throttling doesn't happen.

I don't know if considering IRQ time in some way or another in
sched_rt_runtime_exceeded() really is a way out here.

> Thanks,
>
>         tglx


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WARNING: multiple messages have this Message-ID (diff)
From: Valentin Schneider <valentin.schneider@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Oltean <olteanv@gmail.com>,
	Kurt Kanzenbach <kurt.kanzenbach@linutronix.de>,
	Alison Wang <alison.wang@nxp.com>,
	catalin.marinas@arm.com, will@kernel.org, paulmck@kernel.org,
	mw@semihalf.com, leoyang.li@nxp.com, vladimir.oltean@nxp.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Anna-Maria Gleixner <anna-maria@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting
Date: Mon, 03 Aug 2020 16:47:03 +0100	[thread overview]
Message-ID: <jhjh7tjivew.mognet@arm.com> (raw)
In-Reply-To: <87d047n4oh.fsf@nanos.tec.linutronix.de>


On 03/08/20 16:13, Thomas Gleixner wrote:
> Vladimir Oltean <olteanv@gmail.com> writes:
>>>  1) When irq accounting is disabled, RT throttling kicks in as
>>>     expected.
>>> 
>>>  2) With irq accounting the RT throttler does not kick in and the RCU
>>>     stall/lockups happen.
>> What is this telling us?
>
> It seems that the fine grained irq time accounting affects the runtime
> accounting in some way which I haven't figured out yet.
>

With IRQ_TIME_ACCOUNTING, rq_clock_task() will always be incremented by a
lesser-or-equal value than when not having the option; you start with the
same delta_exec but slice some for the IRQ accounting, and leave the rest
for the rq_clock_task() (+paravirt).

IIUC this means that if you spend e.g. 10% of the time in IRQ and 90% of
the time running the stress-ng RT tasks, despite having RT tasks hogging
the entirety of the "available time" it is still only 90% runtime, which is
below the 95% default and the throttling doesn't happen.

I don't know if considering IRQ time in some way or another in
sched_rt_runtime_exceeded() really is a way out here.

> Thanks,
>
>         tglx


  reply	other threads:[~2020-08-03 15:48 UTC|newest]

Thread overview: 62+ 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  3:39 ` Alison Wang
2020-07-29  8:40 ` Kurt Kanzenbach
2020-07-29  8:40   ` Kurt Kanzenbach
2020-07-29  8:50   ` [EXT] " Alison Wang
2020-07-29  8:50     ` Alison Wang
2020-07-29  9:49   ` Vladimir Oltean
2020-07-29  9:49     ` Vladimir Oltean
2020-07-30  7:23     ` Kurt Kanzenbach
2020-07-30  7:23       ` Kurt Kanzenbach
2020-07-30  8:22       ` Vladimir Oltean
2020-07-30  8:22         ` Vladimir Oltean
2020-08-03  8:04         ` Kurt Kanzenbach
2020-08-03  8:04           ` Kurt Kanzenbach
2020-08-03  8:16           ` Vladimir Oltean
2020-08-03  8:16             ` Vladimir Oltean
2020-08-03  9:51             ` Robin Murphy
2020-08-03  9:51               ` Robin Murphy
2020-08-03 11:38               ` Vladimir Oltean
2020-08-03 11:38                 ` Vladimir Oltean
2020-08-03 11:48                 ` Valentin Schneider
2020-08-03 11:48                   ` Valentin Schneider
2020-08-03 13:24                   ` Marc Zyngier
2020-08-03 13:24                     ` Marc Zyngier
2020-08-03 10:02             ` Thomas Gleixner
2020-08-03 10:02               ` Thomas Gleixner
2020-08-03 10:49           ` Thomas Gleixner
2020-08-03 10:49             ` Thomas Gleixner
2020-08-03 11:41             ` Vladimir Oltean
2020-08-03 11:41               ` Vladimir Oltean
2020-08-03 15:13               ` Thomas Gleixner
2020-08-03 15:13                 ` Thomas Gleixner
2020-08-03 15:47                 ` Valentin Schneider [this message]
2020-08-03 15:47                   ` Valentin Schneider
2020-08-03 16:14                   ` Vladimir Oltean
2020-08-03 16:14                     ` Vladimir Oltean
2020-08-03 19:22                   ` Thomas Gleixner
2020-08-03 19:22                     ` Thomas Gleixner
2020-08-03 23:59                     ` Valentin Schneider
2020-08-03 23:59                       ` Valentin Schneider
2020-08-05  8:50                       ` Dietmar Eggemann
2020-08-05  8:50                         ` Dietmar Eggemann
2020-08-05 13:40                     ` peterz
2020-08-05 13:40                       ` peterz
2020-08-05 13:56                       ` Valentin Schneider
2020-08-05 13:56                         ` Valentin Schneider
2020-08-05 15:31                         ` peterz
2020-08-05 15:31                           ` peterz
2020-08-06  9:41                           ` Thomas Gleixner
2020-08-06  9:41                             ` Thomas Gleixner
2020-08-06 11:45                             ` peterz
2020-08-06 11:45                               ` peterz
2020-08-06 13:27                               ` Paul E. McKenney
2020-08-06 13:27                                 ` Paul E. McKenney
2020-08-06 19:03                                 ` Thomas Gleixner
2020-08-06 19:03                                   ` Thomas Gleixner
2020-08-06 20:39                                   ` Paul E. McKenney
2020-08-06 20:39                                     ` Paul E. McKenney
2020-08-06 18:58                               ` Thomas Gleixner
2020-08-06 18:58                                 ` Thomas Gleixner
2020-08-06  9:34                       ` Thomas Gleixner
2020-08-06  9:34                         ` Thomas Gleixner

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