On Mon, 7 Oct 2019 at 17:14, Rik van Riel <r...@surriel.com> wrote: > > On Thu, 2019-09-19 at 09:33 +0200, Vincent Guittot wrote: > > runnable load has been introduced to take into account the case where > > blocked load biases the wake up path which may end to select an > > overloaded > > CPU with a large number of runnable tasks instead of an underutilized > > CPU with a huge blocked load. > > > > Tha wake up path now starts to looks for idle CPUs before comparing > > runnable load and it's worth aligning the wake up path with the > > load_balance. > > > > Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> > > On a single socket system, patches 9 & 10 have the > result of driving a woken up task (when wake_wide is > true) to the CPU core with the lowest blocked load, > even when there is an idle core the task could run on > right now. > > With the whole series applied, I see a 1-2% regression > in CPU use due to that issue. > > With only patches 1-8 applied, I see a 1% improvement in > CPU use for that same workload.
Thanks for testing. patch 8-9 have just replaced runnable load by blocked load and then removed the duplicated metrics in find_idlest_group. I'm preparing an additional patch that reworks find_idlest_group() to behave similarly to find_busiest_group(). It gathers statistics what it already does, then classifies the groups and finally selects the idlest one. This should fix the problem that you mentioned above when it selects a group with lowest blocked load whereas there are idle cpus in another group with high blocked load. > > Given that it looks like select_idle_sibling and > find_idlest_group_cpu do roughly the same thing, I > wonder if it is enough to simply add an additional > test to find_idlest_group to have it return the > LLC sg, if it is called on the LLC sd on a single > socket system. That make sense to me > > That way find_idlest_group_cpu can still find an > idle core like it does today. > > Does that seem like a reasonable thing? That's worth testing > > I can run tests with that :) > > -- > All Rights Reversed.