From: Avi Kivity <avi@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>,
Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>,
Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org, vatsa@linux.vnet.ibm.com,
bharata@linux.vnet.ibm.com
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS
Date: Wed, 04 Jan 2012 23:41:29 +0200 [thread overview]
Message-ID: <4F04C789.40209@redhat.com> (raw)
In-Reply-To: <1325712710.3084.10.camel@laptop>
On 01/04/2012 11:31 PM, Peter Zijlstra wrote:
> On Wed, 2012-01-04 at 19:16 +0200, Avi Kivity wrote:
> >
> >
> > I think we can solve it at the guest level. The paravirt ticketlock
> > stuff introduces wait/wake calls (actually wait is just a HLT
> > instruction); we could spin for a while, then HLT until the other side
> > wakes us. We should do this for all sites that busy wait.
> >
> This is all TLB invalidates, right?
>
> So why wait for non-running vcpus at all? That is, why not paravirt the
> TLB flush such that the invalidate marks the non-running VCPU's state so
> that on resume it will first flush its TLBs. That way you don't have to
> wake it up and wait for it to invalidate its TLBs.
That's what Xen does, but it's tricky. For example
get_user_pages_fast() depends on the IPI to hold off page freeing, if we
paravirt it we have to take that into consideration.
> Or am I like totally missing the point (I am after all reading the
> thread backwards and I haven't yet fully paged the kernel stuff back
> into my brain).
You aren't, and I bet those kernel pages are unswappable anyway.
> I guess tagging remote VCPU state like that might be somewhat tricky..
> but it seems worth considering, the whole wake and wait for flush thing
> seems daft.
It's nasty, but then so is paravirt. It's hard to get right, and it has
a tendency to cause performance regressions as hardware improves.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2012-01-04 21:41 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-19 8:33 [RFC PATCH 0/4] Gang scheduling in CFS Nikunj A. Dadhania
2011-12-19 8:34 ` [RFC PATCH 1/4] sched: Adding cpu.gang file to cpu cgroup Nikunj A. Dadhania
2011-12-19 8:34 ` [RFC PATCH 2/4] sched: Adding gang scheduling infrastrucure Nikunj A. Dadhania
2011-12-19 15:51 ` Peter Zijlstra
2011-12-19 16:51 ` Peter Zijlstra
2011-12-20 1:43 ` Nikunj A Dadhania
2011-12-20 1:39 ` Nikunj A Dadhania
2011-12-19 8:34 ` [RFC PATCH 3/4] sched: Gang using set_next_buddy Nikunj A. Dadhania
2011-12-19 8:35 ` [RFC PATCH 4/4] sched:Implement set_gang_buddy Nikunj A. Dadhania
2011-12-19 15:51 ` Peter Zijlstra
2011-12-20 1:43 ` Nikunj A Dadhania
2011-12-26 2:30 ` Nikunj A Dadhania
2011-12-19 11:23 ` [RFC PATCH 0/4] Gang scheduling in CFS Ingo Molnar
2011-12-19 11:44 ` Avi Kivity
2011-12-19 11:50 ` Nikunj A Dadhania
2011-12-19 11:59 ` Avi Kivity
2011-12-19 12:06 ` Nikunj A Dadhania
2011-12-19 12:50 ` Avi Kivity
2011-12-19 13:09 ` Nikunj A Dadhania
2011-12-19 11:45 ` Nikunj A Dadhania
2011-12-19 13:22 ` Nikunj A Dadhania
2011-12-19 16:28 ` Ingo Molnar
2011-12-21 10:39 ` Nikunj A Dadhania
2011-12-21 10:43 ` Avi Kivity
2011-12-23 3:20 ` Nikunj A Dadhania
2011-12-23 10:36 ` Ingo Molnar
2011-12-25 10:58 ` Avi Kivity
2011-12-25 15:45 ` Avi Kivity
2011-12-26 3:14 ` Nikunj A Dadhania
2011-12-26 9:05 ` Avi Kivity
2011-12-26 11:33 ` Nikunj A Dadhania
2011-12-26 11:41 ` Avi Kivity
2011-12-27 1:47 ` Nikunj A Dadhania
2011-12-27 9:15 ` Avi Kivity
2011-12-27 10:24 ` Nikunj A Dadhania
2011-12-29 16:07 ` Better qemu/kvm defaults (was Re: [RFC PATCH 0/4] Gang scheduling in CFS) Dor Laor
2011-12-29 16:07 ` [Qemu-devel] " Dor Laor
2011-12-29 16:13 ` Avi Kivity
2011-12-29 16:13 ` [Qemu-devel] " Avi Kivity
2011-12-29 16:16 ` Anthony Liguori
2011-12-29 16:16 ` Anthony Liguori
2012-01-01 10:16 ` Dor Laor
2012-01-01 10:16 ` [Qemu-devel] " Dor Laor
2012-01-01 14:01 ` Ronen Hod
2012-01-01 14:01 ` Ronen Hod
2012-01-02 9:37 ` Dor Laor
2012-01-02 9:37 ` [Qemu-devel] " Dor Laor
2012-01-03 15:48 ` Anthony Liguori
2012-01-03 15:48 ` Anthony Liguori
2012-01-03 22:31 ` Dor Laor
2012-01-03 22:31 ` Dor Laor
2012-01-03 22:45 ` Anthony Liguori
2012-01-03 22:45 ` [Qemu-devel] " Anthony Liguori
2012-01-03 22:59 ` Dor Laor
2012-01-03 22:59 ` Dor Laor
2011-12-27 3:15 ` [RFC PATCH 0/4] Gang scheduling in CFS Nikunj A Dadhania
2011-12-27 9:17 ` Avi Kivity
2011-12-27 9:44 ` Nikunj A Dadhania
2011-12-27 9:51 ` Avi Kivity
2011-12-27 10:10 ` Nikunj A Dadhania
2011-12-27 10:34 ` Avi Kivity
2011-12-27 10:43 ` Nikunj A Dadhania
2011-12-27 10:53 ` Avi Kivity
2011-12-30 9:51 ` Ingo Molnar
2011-12-30 10:10 ` Nikunj A Dadhania
2011-12-31 2:21 ` Nikunj A Dadhania
2012-01-02 4:20 ` Nikunj A Dadhania
2012-01-02 9:39 ` Avi Kivity
2012-01-02 10:22 ` Nikunj A Dadhania
2012-01-02 9:37 ` Avi Kivity
2012-01-02 10:30 ` Nikunj A Dadhania
2012-01-02 13:33 ` Avi Kivity
2012-01-04 10:52 ` Nikunj A Dadhania
2012-01-04 14:41 ` Avi Kivity
2012-01-04 14:56 ` Srivatsa Vaddagiri
2012-01-04 17:13 ` Avi Kivity
2012-01-05 6:57 ` Nikunj A Dadhania
2012-01-04 16:47 ` Rik van Riel
2012-01-04 17:16 ` Avi Kivity
2012-01-04 20:56 ` Rik van Riel
2012-01-04 21:31 ` Peter Zijlstra
2012-01-04 21:41 ` Avi Kivity [this message]
2012-01-05 9:10 ` Ingo Molnar
2012-02-20 8:08 ` Nikunj A Dadhania
2012-02-20 8:14 ` Ingo Molnar
2012-02-20 10:51 ` Peter Zijlstra
2012-02-20 11:53 ` Nikunj A Dadhania
2012-02-20 12:02 ` Srivatsa Vaddagiri
2012-02-20 12:14 ` Peter Zijlstra
2012-01-05 2:10 ` Nikunj A Dadhania
2011-12-19 15:51 ` Peter Zijlstra
2011-12-19 16:09 ` Alan Cox
2011-12-19 22:10 ` Benjamin Herrenschmidt
2011-12-20 1:56 ` Nikunj A Dadhania
2011-12-20 8:52 ` Jeremy Fitzhardinge
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