linux-kernel - [PATCH 0/2] sched/eevdf: sched_attr::sched

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Date:   Fri, 15 Sep 2023 14:43:54 +0200
From:   peterz@...radead.org
To:     mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        vincent.guittot@...aro.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, corbet@....net,
        qyousef@...alina.io, chris.hyser@...cle.com,
        patrick.bellasi@...bug.net, pjt@...gle.com, pavel@....cz,
        qperret@...gle.com, tim.c.chen@...ux.intel.com, joshdon@...gle.com,
        timj@....org, kprateek.nayak@....com, yu.c.chen@...el.com,
        youssefesmat@...omium.org, joel@...lfernandes.org, efault@....de,
        tglx@...utronix.de, daniel.m.jordan@...cle.com
Subject: [PATCH 0/2] sched/eevdf: sched_attr::sched_runtime slice hint

Hi,

As promised a while ago, here is a new version of the variable slice length
hint stuff.  Back when I asked for comments on the latency-nice vs slice length
thing, there was very limited feedback on-list, a number of people have
expressed interrest in the slice length hint.


I'm still working on improving the wakeup latency -- but esp. after commit:

  63304558ba5d ("sched/eevdf: Curb wakeup-preemption")

it needs a little more work. Everything I tried so far made it worse.

As is it behaves ok-ish:

  root@...-ep:~/bench# cat doit-latency-slice.sh
  #!/bin/bash

  perf bench sched messaging -g 40 -l 12000 &

  sleep 1
  chrt3 -o --sched-runtime $((`cat /debug/sched/base_slice_ns`*10)) 0 cyclictest --policy other -D 5 -q   -H 20000 --histfile data.txt ; grep Latencies data.txt
  chrt3 -o --sched-runtime 0 0 cyclictest --policy other -D 5 -q   -H 20000 --histfile data.txt ; grep Latencies data.txt
  chrt3 -o --sched-runtime $((`cat /debug/sched/base_slice_ns`/10)) 0 cyclictest --policy other -D 5 -q   -H 20000 --histfile data.txt ; grep Latencies data.txt

  wait $!
  root@...-ep:~/bench# ./doit-latency-slice.sh
  # Running 'sched/messaging' benchmark:
  # /dev/cpu_dma_latency set to 0us
  # Min Latencies: 00060
  # Avg Latencies: 00990
  # Max Latencies: 224925
  # /dev/cpu_dma_latency set to 0us
  # Min Latencies: 00020
  # Avg Latencies: 00656
  # Max Latencies: 37595
  # /dev/cpu_dma_latency set to 0us
  # Min Latencies: 00016
  # Avg Latencies: 00354
  # Max Latencies: 16687
  # 20 sender and receiver processes per group
  # 40 groups == 1600 processes run

       Total time: 38.246 [sec]


(chrt3 is a hacked up version of util-linux/chrt that allows --sched-runtime unconditionally)