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 20:43:03 +0530 Subject: [PATCH 1/2] ARM: KVM: Yield CPU when vcpu executes a WFE In-Reply-To: <52541F93.4070503@arm.com> References: <1381160430-11790-1-git-send-email-marc.zyngier@arm.com> <1381160430-11790-2-git-send-email-marc.zyngier@arm.com> <5253FDDD.6050008@arm.com> <52541EA3.7010403@linux.vnet.ibm.com> <52541F93.4070503@arm.com> Message-ID: <525420FF.30503@linux.vnet.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 10/08/2013 08:36 PM, Marc Zyngier wrote: >>> 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. > > Only 2x overcommit (dual core host, quad vcpu guests). Okay. quad vcpu seem to explain. > >> RELAX_INTERCEPT is worth enabling for large guests with >> overcommits. > > I'll try something more aggressive as soon as I get the time. What do > you call a large guest? So far, the hard limit on ARM is 8 vcpus. > Okay. I was referring to guests >= 32 vcpus. May be 8vcpu guests with 2x/4x is worth trying. If we still do not see benefit, then it is not worth enabling.