Messages in this thread Patch in this message | | | Date | Thu, 28 Jan 2016 16:31:11 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable) again and shut down on idle) |
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On Wed 27-01-16 12:26:16, Christoph Lameter wrote: > On Wed, 27 Jan 2016, Michal Hocko wrote: [...] > > +void quiet_vmstat(void) > > +{ > > + if (system_state != SYSTEM_RUNNING) > > + return; > > + > > + /* > > + * If we are already in hands of the shepherd then there > > + * is nothing for us to do here. > > + */ > > + if (cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off)) > > + return; > > + > > + if (!need_update(smp_processor_id())) > > + return; > > + > > + /* > > + * Just refresh counters and do not care about the pending delayed > > + * vmstat_update. It doesn't fire that often to matter and canceling > > + * it would be too expensive from this path. > > + * vmstat_shepherd will take care about that for us. > > + */ > > + refresh_cpu_vm_stats(false); > > +} > > The problem here is that there will be an additional tick generated on > idle. This is an issue for power because now the processor has to > needlessly wake up again, do tick processing etc just to effectively do a > cancel_delayed_work().
Thinking about it some more, making vmstat_update deferrable should help to not interrupt idle no? --- diff --git a/mm/vmstat.c b/mm/vmstat.c index eb30bf45bd55..69537d2be6f6 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1512,7 +1512,7 @@ static void __init start_shepherd_timer(void) int cpu; for_each_possible_cpu(cpu) - INIT_DELAYED_WORK(per_cpu_ptr(&vmstat_work, cpu), + INIT_DEFERRABLE_WORK(per_cpu_ptr(&vmstat_work, cpu), vmstat_update); if (!alloc_cpumask_var(&cpu_stat_off, GFP_KERNEL)) -- Michal Hocko SUSE Labs
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