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

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Message-ID: <5509E1D3.7040109@hp.com>
Date:	Wed, 18 Mar 2015 16:36:35 -0400
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	paolo.bonzini@...il.com, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, paulmck@...ux.vnet.ibm.com,
	riel@...hat.com, torvalds@...ux-foundation.org,
	raghavendra.kt@...ux.vnet.ibm.com, david.vrabel@...rix.com,
	oleg@...hat.com, scott.norton@...com, doug.hatch@...com,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	luto@...capital.net
Subject: Re: [PATCH 0/9] qspinlock stuff -v15

On 03/16/2015 09:16 AM, 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!).
>
> 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.
>
> Of course; once this lands people can look at improving the paravirt nonsense.
>

Thanks for sending this out. I have no problem with the !paravirt patch. 
I do have some comments on the paravirt one which I will reply individually.

Cheers,
Longman
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