Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 20 Feb 2015 15:13:21 +0100 | Subject | Re: [PATCH RESEND v9 00/10] sched: consolidation of CPU capacity and usage |
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On 20 February 2015 at 12:52, Morten Rasmussen <morten.rasmussen@arm.com> wrote: > On Fri, Feb 20, 2015 at 11:34:47AM +0000, Peter Zijlstra wrote: >> On Thu, Feb 19, 2015 at 12:49:40PM +0000, Morten Rasmussen wrote: >> >> > Also, it still not clear why patch 10 uses relative capacity reduction >> > instead of absolute capacity available to CFS tasks. >> >> As present in your asymmetric big and small systems? Yes it would be >> unfortunate to migrate a task to an idle small core when the big core is >> still faster, even if reduced by rt/irq work. > > Yes, exactly. I don't think it would cause any harm for symmetric cases > to use absolute capacity instead. Am I missing something?
If absolute capacity is used, we will trig an active load balance from little to big core each time a little has got 1 task and a big core is idle whereas we only want to trig an active migration is the src_cpu's capacity that is available for the cfs task is significantly reduced by rt tasks.
I can mix absolute and relative tests by 1st testing that the capacity of the src is reduced and then ensure that the dst_cpu has more absolute capacity than src_cpu
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