Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting | Date | Mon, 03 Aug 2020 21:22:53 +0200 |
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Valentin,
Valentin Schneider <valentin.schneider@arm.com> writes: > 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.
totaltime = irqtime + tasktime
Ignoring irqtime and pretending that totaltime is what the scheduler can control and deal with is naive at best.
Thanks,
tglx
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