Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1037687AbdDUKFP (ORCPT ); Fri, 21 Apr 2017 06:05:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:44876 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1037541AbdDUKFO (ORCPT ); Fri, 21 Apr 2017 06:05:14 -0400 Subject: Re: [PATCH v6] kvm: better MWAIT emulation for guests To: Paolo Bonzini , "Michael S. Tsirkin" References: <1491911135-216950-1-git-send-email-agraf@suse.de> <4622E361-52AB-40F2-9915-45C48F0DBCD2@suse.de> <204f274d-697d-f9c6-8719-9bf91105f8b9@suse.de> <20170412185249-mutt-send-email-mst@kernel.org> Cc: Jim Mattson , kvm list , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , LKML , "Gabriel L. Somlo" , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , the arch/x86 maintainers , Joerg Roedel , linux-doc@vger.kernel.org, qemu-devel@nongnu.org From: Alexander Graf Message-ID: <03f26e4b-6355-602a-f817-2c1ab38de199@suse.de> Date: Fri, 21 Apr 2017 12:05:10 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1174 Lines: 33 On 21.04.17 12:02, Paolo Bonzini wrote: > > > On 12/04/2017 18:29, Michael S. Tsirkin wrote: >> I don't really agree we do not need the PV flag. mwait on kvm is >> different from mwait on bare metal in that you are heavily penalized by >> scheduler for polling unless you configure the host just so. >> HLT lets you give up the host CPU if you know you won't need >> it for a long time. >> >> So while many people can get by with monitor cpuid (those that isolate >> host CPUs) and it's a valuable option to have, I think a PV flag is also >> a valuable option and can be set for more configurations. >> >> Guest has an idle driver calling mwait on short waits and halt on longer >> ones. I'm in fact testing an idle driver using such a PV flag and will >> post when ready (after vacation ~3 weeks from now probably). > > For now I think I'm removing the PV flag, making this just an > optimization of commit 87c00572ba05aa8c ("kvm: x86: emulate > monitor and mwait instructions as nop"). > > We can add it for 4.13 together with the idle driver. I think that's a perfectly reasonable approach, yes. We can always add the PV flag with the driver. Thanks a lot! Alex