Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm

From: Christian Borntraeger
Date: Wed Sep 16 2015 - 04:57:59 EST


Am 16.09.2015 um 10:32 schrieb Paolo Bonzini:
>
>
> On 15/09/2015 19:38, Paul E. McKenney wrote:
>> Excellent points!
>>
>> Other options in such situations include the following:
>>
>> o Rework so that the code uses call_rcu*() instead of *_expedited().
>>
>> o Maintain a per-task or per-CPU counter so that every so many
>> *_expedited() invocations instead uses the non-expedited
>> counterpart. (For example, synchronize_rcu instead of
>> synchronize_rcu_expedited().)
>
> Or just use ratelimit (untested):

One of my tests was to always replace synchronize_sched_expedited with
synchronize_sched and things turned out to be even worse. Not sure if
it makes sense to test yopur in-the-middle approach?

Christian

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