From: Tejun Heo <tj@kernel.org>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
"linux-kernel@vger.kernel.org >> Linux Kernel Mailing List"
<linux-kernel@vger.kernel.org>, KVM list <kvm@vger.kernel.org>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm
Date: Wed, 16 Sep 2015 07:03:51 -0400 [thread overview]
Message-ID: <20150916110351.GA17047@htj.duckdns.org> (raw)
In-Reply-To: <55F94B38.5060308@de.ibm.com>
Hello,
On Wed, Sep 16, 2015 at 12:58:00PM +0200, Christian Borntraeger wrote:
> FWIW, I added a printk to percpu_down_write. With KVM and uprobes disabled,
> just booting up a fedora20 gives me __6749__ percpu_down_write calls on 4.2.
> systemd seems to do that for the processes.
>
> So a revert is really the right thing to do. In fact, I dont know if the
> rcu_sync_enter rework is enough. With systemd setting the cgroup seem to
> be NOT a cold/seldom case.
Booting would usually be the hottest operation for that and it's still
*relatively* cold path compared to the reader side which is task
fork/exit paths. The whole point is shift overhead from hotter reader
side. Can you see problems with percpu_rwsem rework?
Thanks.
--
tejun
next prev parent reply other threads:[~2015-09-16 11:03 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-15 12:05 [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm Christian Borntraeger
2015-09-15 13:05 ` Peter Zijlstra
2015-09-15 13:36 ` Christian Borntraeger
2015-09-15 13:53 ` Tejun Heo
2015-09-15 16:42 ` Paolo Bonzini
2015-09-15 17:38 ` Paul E. McKenney
2015-09-16 8:32 ` Paolo Bonzini
2015-09-16 8:57 ` Christian Borntraeger
2015-09-16 9:12 ` Paolo Bonzini
2015-09-16 12:22 ` Oleg Nesterov
2015-09-16 12:35 ` Paolo Bonzini
2015-09-16 12:43 ` Oleg Nesterov
2015-09-16 12:56 ` Christian Borntraeger
2015-09-16 14:16 ` Tejun Heo
2015-09-16 14:19 ` Paolo Bonzini
2015-09-15 21:11 ` Christian Borntraeger
2015-09-15 21:26 ` Tejun Heo
2015-09-15 21:38 ` Paul E. McKenney
2015-09-15 22:28 ` Tejun Heo
2015-09-15 23:38 ` Paul E. McKenney
2015-09-16 1:24 ` Tejun Heo
2015-09-16 4:35 ` Paul E. McKenney
2015-09-16 11:06 ` Tejun Heo
2015-09-16 7:44 ` Christian Borntraeger
2015-09-16 10:58 ` Christian Borntraeger
2015-09-16 11:03 ` Tejun Heo [this message]
2015-09-16 11:50 ` Christian Borntraeger
2015-09-16 15:55 ` [PATCH cgroup/for-4.3-fixes 1/2] Revert "cgroup: simplify threadgroup locking" Tejun Heo
2015-09-16 15:56 ` [PATCH cgroup/for-4.3-fixes 2/2] Revert "sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem" Tejun Heo
2015-09-16 17:00 ` [PATCH cgroup/for-4.3-fixes 1/2] Revert "cgroup: simplify threadgroup locking" Oleg Nesterov
2015-09-16 18:45 ` Christian Borntraeger
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