linux-kernel - Re: [Xen-devel] [PATCH 0/9] qspinlock stuff -v15

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Date:	Mon, 16 Mar 2015 14:08:58 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Peter Zijlstra <peterz@...radead.org>, <Waiman.Long@...com>
CC:	<raghavendra.kt@...ux.vnet.ibm.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>,
	<boris.ostrovsky@...cle.com>, <linux-arch@...r.kernel.org>,
	<x86@...nel.org>, <mingo@...hat.com>, <doug.hatch@...com>,
	<xen-devel@...ts.xenproject.org>, <paulmck@...ux.vnet.ibm.com>,
	<riel@...hat.com>, <scott.norton@...com>,
	<paolo.bonzini@...il.com>, <tglx@...utronix.de>,
	<virtualization@...ts.linux-foundation.org>, <oleg@...hat.com>,
	<luto@...capital.net>, <david.vrabel@...rix.com>,
	<torvalds@...ux-foundation.org>
Subject: Re: [Xen-devel] [PATCH 0/9] qspinlock stuff -v15

On 16/03/15 13:16, Peter Zijlstra wrote:
> Hi Waiman,
> 
> As promised; here is the paravirt stuff I did during the trip to BOS last week.
> 
> All the !paravirt patches are more or less the same as before (the only real
> change is the copyright lines in the first patch).
> 
> The paravirt stuff is 'simple' and KVM only -- the Xen code was a little more
> convoluted and I've no real way to test that but it should be stright fwd to
> make work.
> 
> I ran this using the virtme tool (thanks Andy) on my laptop with a 4x
> overcommit on vcpus (16 vcpus as compared to the 4 my laptop actually has) and
> it both booted and survived a hackbench run (perf bench sched messaging -g 20
> -l 5000).
> 
> So while the paravirt code isn't the most optimal code ever conceived it does work.
> 
> Also, the paravirt patching includes replacing the call with "movb $0, %arg1"
> for the native case, which should greatly reduce the cost of having
> CONFIG_PARAVIRT_SPINLOCKS enabled on actual hardware.
> 
> I feel that if someone were to do a Xen patch we can go ahead and merge this
> stuff (finally!).

I can look at this.  It looks pretty straight-forward.

> These patches do not implement the paravirt spinlock debug stats currently
> implemented (separately) by KVM and Xen, but that should not be too hard to do
> on top and in the 'generic' code -- no reason to duplicate all that.

I think this is fine.

David
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