linux-kernel - Re: [PATCH 1/2] sched: add virt sched domain for the guest

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] [day] [month] [year] [list]

Message-ID: <1337788367.9783.12.camel@laptop>
Date:	Wed, 23 May 2012 17:52:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Liu ping fan <kernelfans@...il.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
	Ingo Molnar <mingo@...hat.com>, Avi Kivity <avi@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [PATCH 1/2] sched: add virt sched domain for the guest

On Wed, 2012-05-23 at 08:23 -0700, Dave Hansen wrote:
> On 05/23/2012 01:48 AM, Peter Zijlstra wrote:
> > On Wed, 2012-05-23 at 16:34 +0800, Liu ping fan wrote:
> >> > so we need to migrate some of vcpus from node-B to node-A, or to
> >> > node-C.
> > This is absolutely broken, you cannot do that.
> > 
> > A guest task might want to be node affine, it looks at the topology sets
> > a cpu affinity mask and expects to stay on that node.
> > 
> > But then you come along, and flip one of those cpus to another node. The
> > guest task will now run on another node and get remote memory accesses.
> 
> Insane, sure.  But, if the node has physically gone away, what do we do?
>  I think we've got to either kill the guest, or let it run somewhere
> suboptimal.  Sounds like you're advocating killing it. ;)

You all seem terribly confused. If you want a guest that 100% mirrors
the host topology you need hard-binding of all vcpu threads and clearly
you're in trouble if you unplug a host cpu while there's still a vcpu
expecting to run there.

That's an administrator error and you get to keep the pieces, I don't
care.

In case you want simple virt-numa where a number of vcpus constitute a
vnode and have their memory all on the same node the vcpus are ran on,
what does it matter if you unplug something in the host? Just migrate
everything -- including memory.

But what Liu was proposing is completely insane and broken. You cannot
simply remap cpu:node relations. Wanting to do that shows a profound
lack of understanding.

Our kernel assumes that a cpu remains on the same node. All userspace
that does anything with NUMA assumes the same. You cannot change this.

--
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/