Messages in this thread |  | | Date | Tue, 11 Dec 2012 13:28:02 +0800 | From | Alex Shi <> | Subject | Re: [PATCH 01/18] sched: select_task_rq_fair clean up |
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On 12/11/2012 12:23 PM, Preeti U Murthy wrote: > Hi Alex, > > On 12/10/2012 01:52 PM, Alex Shi wrote: >> It is impossible to miss a task allowed cpu in a eligible group. > > The one thing I am concerned with here is if there is a possibility of > the task changing its tsk_cpus_allowed() while this code is running. > > i.e find_idlest_group() finds an idle group,then the tsk_cpus_allowed() > for the task changes,perhaps by the user himself,which might not include > the cpus in the idle group.After this find_idlest_cpu() is called.I mean > a race condition in short.Then we might not have an eligible cpu in that > group right?
your worry make sense, but the code handle the situation, in select_task_rq(), it will check the cpu allowed again. if the answer is no, it will fallback to old cpu. > >> And since find_idlest_group only return a different group which >> excludes old cpu, it's also imporissible to find a new cpu same as old >> cpu. > > This I agree with. > >> Signed-off-by: Alex Shi <alex.shi@intel.com> >> --- >> kernel/sched/fair.c | 5 ----- >> 1 files changed, 0 insertions(+), 5 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 59e072b..df99456 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -3150,11 +3150,6 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) >> } >> >> new_cpu = find_idlest_cpu(group, p, cpu); >> - if (new_cpu == -1 || new_cpu == cpu) { >> - /* Now try balancing at a lower domain level of cpu */ >> - sd = sd->child; >> - continue; >> - } >> >> /* Now try balancing at a lower domain level of new_cpu */ >> cpu = new_cpu; >> > Regards > Preeti U Murthy >
-- Thanks Alex
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