From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753308AbdEPQ6V (ORCPT ); Tue, 16 May 2017 12:58:21 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:36032 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751845AbdEPQ6R (ORCPT ); Tue, 16 May 2017 12:58:17 -0400 Subject: Re: [PATCH] KVM: x86: lower default for halt_poll_ns From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: rkrcmar@redhat.com References: <20170418104118.21719-1-pbonzini@redhat.com> Message-ID: <4385bc02-2456-e8a7-a22b-cc2783ad6822@redhat.com> Date: Tue, 16 May 2017 18:58:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <20170418104118.21719-1-pbonzini@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/04/2017 12:41, Paolo Bonzini wrote: > In some fio benchmarks, halt_poll_ns=400000 caused CPU utilization to > increase heavily even in cases where the performance improvement was > small. In particular, bandwidth divided by CPU usage was as much as > 60% lower. > > To some extent this is the expected effect of the patch, and the > additional CPU utilization is only visible when running the > benchmarks. However, halving the threshold also halves the extra > CPU utilization (from +30-130% to +20-70%) and has no negative > effect on performance. > > Signed-off-by: Paolo Bonzini Ping? Paolo > --- > arch/x86/include/asm/kvm_host.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 74ef58c8ff53..68d4a33da392 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -45,7 +45,7 @@ > > #define KVM_PIO_PAGE_OFFSET 1 > #define KVM_COALESCED_MMIO_PAGE_OFFSET 2 > -#define KVM_HALT_POLL_NS_DEFAULT 400000 > +#define KVM_HALT_POLL_NS_DEFAULT 200000 > > #define KVM_IRQCHIP_NUM_PINS KVM_IOAPIC_NUM_PINS > >