Messages in this thread | | | Date | Wed, 25 Jun 2014 01:39:27 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH 9/7] sched,numa: remove task_h_load from task_numa_compare |
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On 06/25/2014 01:31 AM, Peter Zijlstra wrote: > On Wed, Jun 25, 2014 at 01:25:00AM -0400, Rik van Riel wrote: >> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 >> >> On 06/25/2014 01:21 AM, Peter Zijlstra wrote: >>> On Wed, Jun 25, 2014 at 07:07:35AM +0200, Peter Zijlstra >>> wrote: >>>> Shall I merge this into patch 3? >>> >>> Which gets me the below; which is has a wrong changelog. >>> >>> task_h_load() already computes the load as seen from the root >>> group. effective_load() just does a better (and more expensive) >>> job of computing the task movement implications of a move. >>> >>> So the total effect of this patch shouldn't be very big; >>> regular load balancing also only uses task_h_load(), see >>> move_tasks(). >>> >>> Now, we don't run with preemption disabled, don't run as >>> often, etc.., so maybe we can indeed use the more expensive >>> variant just fine, but does it really matter? >> >> In my testing, it appears to make a difference between workloads >> converging, and workloads sitting with one last thread stuck on >> another node that never gets moved... > > Fair enough; can you provide a new Changelog that I can paste in?
Here it goes:
When CONFIG_FAIR_GROUP_SCHED is enabled, the load that a task places on a CPU is determined by the group the task is in. The active groups on the source and destination CPU can be different, resulting in a different load contribution by the same task at its source and at its destination. As a result, the load needs to be calculated separately for each CPU, instead of estimated once with task_h_load.
Getting this calculation right allows some workloads to converge, where previously the last thread could get stuck on another node, without being able to migrate to its final destination.
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