Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 17 May 2017 09:52:45 +0200 | Subject | Re: [PATCH 1/2] sched: Interrupt Aware Scheduler |
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On 12 May 2017 at 22:19, Rohit Jain <rohit.k.jain@oracle.com> wrote: > On 05/12/2017 12:46 PM, Peter Zijlstra wrote: >> >> On Fri, May 12, 2017 at 11:04:26AM -0700, Rohit Jain wrote: >>> >>> The patch avoids CPUs which might be considered interrupt-heavy when >>> trying to schedule threads (on the push side) in the system. Interrupt >>> Awareness has only been added into the fair scheduling class. >>> >>> It does so by, using the following algorithm: >>> >>> -------------------------------------------------------------------------- >>> 1) When the interrupt is getting processed, the start and the end times >>> are noted for the interrupt on a per-cpu basis. >> >> IRQ_TIME_ACCOUNTING you mean? > > > Yes. Exactly > >>> 2) On a periodic basis the interrupt load is processed for each run >>> queue and this is mapped in terms of percentage in a global array. The >>> interrupt load for a given CPU is also decayed over time, so that the >>> most recent interrupt load has the biggest contribution in the interrupt >>> load calculations. This would mean the scheduler will try to avoid CPUs >>> (if it can) when scheduling threads which have been recently busy with >>> handling hardware interrupts. >> >> You mean like like how its already added to rt_avg? Which is then used >> to lower a CPU's capacity. > > > Right. The only difference I see is that it is not being used on the > enqueue side as of now. > >>> 3) Any CPU which lies above the 80th percentile in terms of percentage >>> interrupt load is considered interrupt-heavy. >>> >>> 4) During idle CPU search from the scheduler perspective this >>> information is used to skip CPUs if better are available. >>> >>> 5) If none of the CPUs are better in terms of idleness and interrupt >>> load, then the interrupt-heavy CPU is considered to be the best >>> available CPU. >> >> I would much rather you work with the EAS people and extend the capacity >> awareness of those code paths. Then, per the existing logic, things >> should just work out. > > > Did you mean we should use the capacity as a metric on the enqueue side > and not introduce a new metric?
If fact, the capacity is already taken into account in the wake up path. you can look at wake_affine(), wake_cap() and capacity_spare_wake() The current implementations takes care of original capacity but it might be extended to take into account capacity stolen by irq/rt as well
> > >> >> It doesn't matter how the capacity is lowered, at some point you just >> don't want to put tasks on. It really doesn't matter if that's because >> IRQs, SoftIRQs, (higher priority) Real-Time tasks, thermal throttling or >> anything else.
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