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