From mboxrd@z Thu Jan  1 00:00:00 1970
From: raghavendra.kt@linux.vnet.ibm.com (Raghavendra K T)
Date: Tue, 08 Oct 2013 20:32:59 +0530
Subject: [PATCH 1/2] ARM: KVM: Yield CPU when vcpu executes a WFE
In-Reply-To: <5253FDDD.6050008@arm.com>
References: <1381160430-11790-1-git-send-email-marc.zyngier@arm.com>
 <1381160430-11790-2-git-send-email-marc.zyngier@arm.com>
 <CAC4Lta14xZNnEUXxZiaF4=PQQTjq4efjsNDAK2oBH4-Uqh_d0A@mail.gmail.com>
 <5253FDDD.6050008@arm.com>
Message-ID: <52541EA3.7010403@linux.vnet.ibm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

[...]
>>> +               kvm_vcpu_on_spin(vcpu);
>>
>> Could you also enable CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT for arm and
>> check if ple handler logic helps further?
>> we would ideally get one more optimization folded into ple handler if
>> you enable that.
>
> Just gave it a go, and the results are slightly (but consistently)
> worse. Over 10 runs:
>
> Without RELAX_INTERCEPT: Average run 3.3623s
> With RELAX_INTERCEPT: Average run 3.4226s
>
> Not massive, but still noticeable. Any clue?

Is it  a 4x overcommit? Probably we would have hit the code
overhead if it were small guests.

RELAX_INTERCEPT is worth enabling for large guests with
overcommits.