linux-kernel - Re: Severe performance regression w/ 4.4+ on Android due to cgroup locking changes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160714174111.GA15816@redhat.com>
Date:	Thu, 14 Jul 2016 19:41:12 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Dmitry Shmidt <dimitrysh@...gle.com>,
	Rom Lemarchand <romlem@...gle.com>,
	Colin Cross <ccross@...gle.com>, Todd Kjos <tkjos@...gle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
	locking changes

On 07/14, John Stultz wrote:
>
> I'm not supposed to be applying this on-top of
> Paul's change, right?

Right, unless I am totally confused,

> > Just in case, could you try the patch below? Of course, without other
> > optimizations from Peter, this change makes cgroup_threadgroup_rwsem
> > much worse than a plain rw_semaphore.
> >
> > Oleg.
> >
> > --- x/kernel/cgroup.c
> > +++ x/kernel/cgroup.c
> > @@ -5605,6 +5605,8 @@ int __init cgroup_init(void)
> >         BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
> >         BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
> >
> > +       rcu_sync_enter(&cgroup_threadgroup_rwsem.rss);
> > +
> 
> 
> So adding this does make a huge difference ontop of Peter's patch.

Ah, sorry for confusion. I meant, you could try this one-liner without
any other changes.

But we will need the "slow mode optimization" part from Peter's patch
anyway, otherwise percpu_rw_semaphore simply makes no sense for
cgroup_threadgroup_rwsem.

Oleg.