Messages in this thread | | | Subject | Re: [PATCH 1/2] sched: Interrupt Aware Scheduler | From | Rohit Jain <> | Date | Fri, 12 May 2017 13:19:50 -0700 |
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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?
> > 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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