From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753012AbbANSWu (ORCPT ); Wed, 14 Jan 2015 13:22:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41777 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750965AbbANSWt (ORCPT ); Wed, 14 Jan 2015 13:22:49 -0500 Message-ID: <54B6B3F3.2000908@redhat.com> Date: Wed, 14 Jan 2015 13:22:43 -0500 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Marcelo Tosatti , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org CC: Luiz Capitulino , Steven Rostedt , Thomas Gleixner , kvm@vger.kernel.org, Paolo Bonzini Subject: Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq References: <20150114171251.882318257@redhat.com> <20150114171459.593877145@redhat.com> In-Reply-To: <20150114171459.593877145@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/14/2015 12:12 PM, Marcelo Tosatti wrote: > The problem: > > On -RT, an emulated LAPIC timer instances has the following path: > > 1) hard interrupt > 2) ksoftirqd is scheduled > 3) ksoftirqd wakes up vcpu thread > 4) vcpu thread is scheduled > > This extra context switch introduces unnecessary latency in the > LAPIC path for a KVM guest. > This patch reduces the average latency in my tests from 14us to 11us. > > Signed-off-by: Marcelo Tosatti Acked-by: Rik van Riel