From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752676Ab1KAT6g (ORCPT ); Tue, 1 Nov 2011 15:58:36 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:56057 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751704Ab1KAT6e (ORCPT ); Tue, 1 Nov 2011 15:58:34 -0400 Message-ID: <4EB04F5F.4010709@us.ibm.com> Date: Tue, 01 Nov 2011 14:58:23 -0500 From: Anthony Liguori User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.21) Gecko/20110831 Lightning/1.0b2 Thunderbird/3.1.13 MIME-Version: 1.0 To: Eric B Munson CC: avi@redhat.com, mingo@redhat.com, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, ryanh@linux.vnet.ibm.com Subject: Re: [PATCH 6/6 V2] Add age out of guest paused flag References: <1320091650-24682-1-git-send-email-emunson@mgebm.net> <1320091650-24682-7-git-send-email-emunson@mgebm.net> <4EB049C3.7080206@us.ibm.com> <20111101195111.GA9852@mgebm.net> In-Reply-To: <20111101195111.GA9852@mgebm.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit x-cbid: 11110119-5930-0000-0000-000000CC68C0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/01/2011 02:51 PM, Eric B Munson wrote: > On Tue, 01 Nov 2011, Anthony Liguori wrote: > >> On 10/31/2011 03:07 PM, Eric B Munson wrote: >>> The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft >>> lockup but it can mask real soft lockups if the flag isn't cleared when it is >>> no longer relevant. This patch adds a kvm ioctl that the hypervisor will use >>> when it resumes a guest to start a timer for aging out the flag. The time out >>> will be specified by the hypervisor in the ioctl call. >>> >>> Signed-off-by: Eric B Munson >> >> Why not have the guest clear the flag when it acknowledges it? >> >> The hypervisor would unconditionally set the bit, and the guest >> would do a testandclear to check if the bit is set. I think that >> avoids the whole aging business. >> >> Regards, >> >> Anthony Liguori > > If you have a look at patch 5 of this series, the flag is cleared when the > guest checks the validity of a soft lockup. However, the aging is meant to > cover the case where the guest never sees a soft lockup. We don't want this > flag to be stored for ever and end up delaying real soft lockup messages. With > that case in mind, I thought this was a good/simple compramise. If the guest clears the flag, then I don't think you have to worry about this. Regards, Anthony Liguori