Messages in this thread | | | Subject | Re: [PATCH v4 00/10] sched/fair: rework the CFS load balance | From | Dietmar Eggemann <> | Date | Wed, 30 Oct 2019 17:24:47 +0100 |
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On 30.10.19 15:39, Phil Auld wrote: > Hi Vincent, > > On Mon, Oct 28, 2019 at 02:03:15PM +0100 Vincent Guittot wrote:
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>>> When you say slow versus fast wakeup paths what do you mean? I'm still >>> learning my way around all this code. >> >> When task wakes up, we can decide to >> - speedup the wakeup and shorten the list of cpus and compare only >> prev_cpu vs this_cpu (in fact the group of cpu that share their >> respective LLC). That's the fast wakeup path that is used most of the >> time during a wakeup >> - or start to find the idlest CPU of the system and scan all domains. >> That's the slow path that is used for new tasks or when a task wakes >> up a lot of other tasks at the same time
[...]
Is the latter related to wake_wide()? If yes, is the SD_BALANCE_WAKE flag set on the sched domains on your machines? IMHO, otherwise those wakeups are not forced into the slowpath (if (unlikely(sd))?
I had this discussion the other day with Valentin S. on #sched and we were not sure how SD_BALANCE_WAKE is set on sched domains on !SD_ASYM_CPUCAPACITY systems.
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