Messages in this thread | | | Date | Thu, 18 Jan 2018 10:38:07 +0000 | From | Morten Rasmussen <> | Subject | Re: [RFC PATCH 2/5] sched: Add NOHZ_STATS_KICK |
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On Mon, Jan 15, 2018 at 09:26:09AM +0100, Vincent Guittot wrote: > Le Wednesday 03 Jan 2018 à 10:16:00 (+0100), Vincent Guittot a écrit : > > Hi Peter, > > > > On 22 December 2017 at 21:42, Peter Zijlstra <peterz@infradead.org> wrote: > > > On Fri, Dec 22, 2017 at 07:56:29PM +0100, Peter Zijlstra wrote: > > >> Right; but I figured we'd try and do it 'right' and see how horrible it > > >> is before we try and do funny things. > > > > > > So now it should have a 32ms tick for up to .5s when the system goes > > > completely idle. > > > > > > No idea how bad that is.. > > > > I have tested your branch but the timer doesn't seem to fire correctly > > because i can still see blocked load in the use case i have run. > > I haven't found the reason yet > > Hi Peter, > > With the patch below on top of your branch, the blocked loads are updated and > decayed regularly. The main differences are: > - It doesn't use a timer to trig ilb but the tick and when a cpu becomes idle. > The main drawback of this solution is that the load is blocked when the > system is fully idle with the advantage of not waking up a fully idle > system. We have to wait for the next tick or newly idle event for updating > blocked load when the system leaves idle stat which can be up to a tick long. > If this is too long, we can check for kicking ilb when task wakes up so the > blocked load will be updated as soon as the system leaves idle state. > The main advantage is that we don't wake up a fully idle system every 32ms to > update blocked load that will be not used. > - I'm working on one more improvement to use nohz_idle_balance in the newly > idle case when the system is not overloaded and > (this_rq->avg_idle > sysctl_sched_migration_cost). In this case, we can try to > use nohz_idle_balance with NOHZ_STATS_KICK and abort as soon as it exceed > this_rq->avg_idle. This will remove some calls to kick_ilb and some wake up > of an idle cpus.
This sound like what I meant in my other reply :-)
It seems pointless to have a timer to update PELT if the system is completely idle, and when it isn't we can piggy back other events to make the updates happen.
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