Re: 2.6.32.y stable kernel regression with taskset

[Mike Galbraith <efault@gmx.de>]

On Wed, 2010-09-15 at 11:47 -0700, Yinghai Lu wrote:
> found problem with cpuscaling test.
> 
> Under 2.6.32.21   Userspace gov  
> min freq load test time is nearly the same as max freq load test time around  ~16 seconds
> 
> under 2.6.18-194
> min freq load test time is ~40 seconds
> max freq load test time	  is ~ 17 seconds
> 
> the test is 
> 1. set governor for one cpu to userspace
> 2. set freq to min for that cpu
> 3. using taskset to put load test only on that cpu, and get the time for load test.
> 
> so that mean taskset did not put load test on cpu that we want. and other cpu still have ondemand governor and load test get done much faster
> 
> git bisect report:
> 
> c6fc81afa2d7ef2f775e48672693d8a0a8a7325d is the first bad commit
> commit c6fc81afa2d7ef2f775e48672693d8a0a8a7325d
> Author: John Wright <john.wright@hp.com>
> Date:   Tue Apr 13 16:55:37 2010 -0600
> 
>     sched: Fix a race between ttwu() and migrate_task()

Known issue.  There's a sched series for 32-stable in the pipeline.

	-Mike