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

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Message-ID: <20150915222811.GD495@htj.duckdns.org>
Date:	Tue, 15 Sep 2015 18:28:11 -0400
From:	Tejun Heo <tj@...nel.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.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

Hello,

On Tue, Sep 15, 2015 at 02:38:30PM -0700, Paul E. McKenney wrote:
> I did take a shot at adding the rcu_sync stuff during this past merge
> window, but it did not converge quickly enough to make it.  It looks
> quite good for the next merge window.  There have been changes in most
> of the relevant areas, so probably best to just try them and see which
> works best.

Heh, I'm having a bit of trouble following.  Are you saying that the
changes would be too big for -stable?  If so, I'll send out reverts of
the culprit patches and then reapply them for this cycle so that it
can land together with the rcu changes in the next merge window, but
it'd be great to find out whether the rcu changes are enough for the
issue that Christian is seeing to go away.  If not, I'll switch to a
different locking scheme and mark those patches w/ stable tag.

Thanks!

-- 
tejun
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