linux-kernel - Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

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: <20120605220059.GV2388@linux.vnet.ibm.com>
Date:	Tue, 5 Jun 2012 15:00:59 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>, linux-pm <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

On Tue, Jun 05, 2012 at 11:37:21PM +0200, Peter Zijlstra wrote:
> On Tue, 2012-06-05 at 14:29 -0700, Paul E. McKenney wrote:
> > OK, I'll bite...  Why not just use CPU hotplug to expel the timers?
> 
> Currently? Can you say: 'kstopmachine'?

So if CPU hotplug (or whatever you want to call it) stops using
kstopmachine, you are OK with it?

> But its also a question of interface and naming. Do you want to have to
> iterate all cpus in your isolated set, do you want to bring them down
> far enough to physically unplug. Ideally no to both.

For many use cases, it is indeed not necessary to get to a point where
the CPUs could be physically removed from the system.  But CPU-failure
use cases would need the CPU to be fully deactivated.  And many of the
hardware guys tell me that the CPU-failure case will be getting more
common, though I sure hope that they are wrong.

> If you don't bring them down far enough to unplug, should you still be
> calling it hotplug?

I am not too worried about what it is called.  Though "banish to monastery"
would probably be going too far in the other direction.

> Ideally I think there'd be a file in your cpuset which if opened and
> written to will flush all pending bits (timers, workqueues, the lot) and
> return when this is done (and maybe provide O_ASYNC writes to not wait
> for completion).

The mobile guys probably are not too worried about bulk operations yet
because they don't have that many CPUs, but it might be useful elsewhere.

							Thanx, Paul

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/