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Date: Thu, 12 Jul 2012 11:12:28 +0300
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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>,
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        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>,
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        Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>,
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Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler
References: <20120709062012.24030.37154.sendpatchset@codeblue>  <4FFA8E5E.3070108@de.ibm.com> <4FFD422B.9060008@redhat.com>  <4FFD52CD.7040403@de.ibm.com> <4FFD5DA3.3010001@redhat.com> <1342059459.18850.46.camel@pasglop>
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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().

-- 
error compiling committee.c: too many arguments to function