From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler
Date: Thu, 12 Jul 2012 21:24:10 +1000
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To: Avi Kivity <avi@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Marcelo Tosatti <mtosatti@redhat.com>, Ingo Molnar <mingo@redhat.com>, Rik van Riel <riel@redhat.com>, S390 <linux-s390@vger.kernel.org>, Carsten Otte <cotte@de.ibm.com>, KVM <kvm@vger.kernel.org>, chegu vinod <chegu_vinod@hp.com>, "Andrew M. Theurer" <habanero@linux.vnet.ibm.com>, LKML <linux-kernel@vger.kernel.org>, X86 <x86@kernel.org>, Gleb Natapov <gleb@redhat.com>, linux390@de.ibm.com, Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>, Joerg Roedel <joerg.roedel@amd.com>, Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>, Alexander Graf <agraf@suse.de>, Paul Mackerras <paulus@samba.org>
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On Thu, 2012-07-12 at 11:12 +0300, Avi Kivity wrote:
> On 07/12/2012 05:17 AM, Benjamin Herrenschmidt wrote:
> >> ARM doesn't have an instruction for cpu_relax(), so it can't intercept
> >> it.  Given ppc's dislike of overcommit, and the way it implements
> >> cpu_relax() by adjusting hw thread priority, I'm guessing it doesn't
> >> intercept those either, but I'm copying the ppc people in case I'm
> >> wrong.  So it's s390 and x86.
> > 
> > No but our spinlocks call __spin_yield()  (or __rw_yield) which does
> > some paravirt tricks already.
> > 
> > We check if the holder is currently running, and if not, we call the
> > H_CONFER hypercall which can be used to "give" our time slice to the
> > holder.
> > 
> > Our implementation of H_CONFER in KVM is currently a nop though.
> 
> Okay, so you can join the party.  See yield_to() and kvm_vcpu_on_spin().

Thanks ! I'll have a look eventually :-)

Cheers,
Ben.