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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next prev parent reply other threads:[~2020-08-03 15:48 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 [this message]
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
2020-08-06 9:34 ` Thomas Gleixner
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