Messages in this thread | | | Subject | Re: [PATCH 1/2] sched: Interrupt Aware Scheduler | From | Rohit Jain <> | Date | Thu, 18 May 2017 10:24:36 -0700 |
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On 05/17/2017 12:52 AM, Vincent Guittot wrote: > On 12 May 2017 at 22:19, Rohit Jain 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
Thanks, I have a new prototype to account for the stolen capacity, I will send it out once I have more test results.
>>> 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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