linux-kernel - Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu

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Message-ID: <55F92F04.1040706@de.ibm.com>
Date:	Wed, 16 Sep 2015 10:57:40 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, paulmck@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org >> Linux Kernel Mailing List" 
	<linux-kernel@...r.kernel.org>, KVM list <kvm@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace
 signal_struct->group_rwsem with a global percpu_rwsem) causes regression for
 libvirt/kvm

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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