Messages in this thread | | | Subject | Re: [PATCH 07/10] sched/fair: Provide can_migrate_task_llc | From | Valentin Schneider <> | Date | Thu, 1 Nov 2018 11:16:37 +0000 |
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On 31/10/2018 19:14, Peter Zijlstra wrote: > On Mon, Oct 29, 2018 at 07:34:50PM +0000, Valentin Schneider wrote: >> On a sidenote, I find it a bit odd that the exec_start threshold depends on >> sysctl_sched_migration_cost, which to me is more about idle_balance() cost >> than "how long does it take for a previously run task to go cache cold". > > A long long (think 2.6.20 long ago) there was code that did boot-time > measurement of the various cache topology costs and that threshold was > related to that. > > That code got killed because of boot to boot variance and dubious > benefits. > > The migration cost is what it was replaced with as a single measure. > > migration cost was then later abused in the newidle balance because it > was over eager.
Thanks! I tried following the blame rabbit hole but got a bit lost along the way.
> Ideally we'd get rid of it there, because we've now got > that much more elaborate accounting, but Rohit tried and found some > regression because of that. > > Maybe we should remove it from newidle anyway. >
Well, if we ditch idle_balance() in favor of stealing, that would "solve" it...
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