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Date: Thu, 12 Jul 2012 14:02:33 +0530
From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Organization: IBM
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To: Avi Kivity <avi@redhat.com>
CC: Christian Borntraeger <borntraeger@de.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>,
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        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
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        Alexander Graf <agraf@suse.de>, Paul Mackerras <paulus@samba.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
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> <4FFD6100.8050202@de.ibm.com> <4FFD65E0.500@redhat.com> <4FFE5C9C.9070001@linux.vnet.ibm.com> <4FFE86A4.2010809@redhat.com>
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On 07/12/2012 01:41 PM, Avi Kivity wrote:
> On 07/12/2012 08:11 AM, Raghavendra K T wrote:
>>> Ah, I thouht you objected to the CONFIG var.  Maybe call it
>>> cpu_relax_intercepted since that's the linuxy name for the instruction.
>>>
>>
>> Ok, just to be on same page. 'll have :
>> 1. cpu_relax_intercepted instead of  pause_loop_exited.
>>
>> 2. CONFIG_KVM_HAVE_CPU_RELAX_INTERCEPT which is unconditionally
>> selected for x86 and s390
>>
>> 3. make request mechanism to clear cpu_relax_intercepted.
>>
>> ('ll do same thing for s390 also but have not seen s390 code using
>> request mechanism, so not sure if it ok.. otherwise we have to clear
>> unconditionally for s390 before guest enter and for x86 we have to move
>> make_request back to vmx/svm).
>> will post V3 with these changes.
>
> You can leave the s390 changes to the s390 people; just make sure the
> generic code is ready.
>
Yep,
Checked the following logic with make_request and it works fine,

vcpu_spin()
{
  ple_exited = true;
.
.
make_request(KVM_REQ_CLEAR_PLE, vcpu);
}

vcpu_enter_guest()
{
  if(check_request(KVM_REQ_CLEAR_PLE))
     ple_exited = false;
.
.
}

But there is following approach that is working perfectly fine.
vcpu_spin()
{
  ple_exited = true;
.
.

  ple_exited = false;
}

I hope to go with second approach. let me know if you find any loop
hole.