From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH 6/6 V2] Add age out of guest paused flag Date: Tue, 01 Nov 2011 14:58:23 -0500 Message-ID: <4EB04F5F.4010709@us.ibm.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from e5.ny.us.ibm.com ([32.97.182.145]:56056 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751896Ab1KAT6e (ORCPT ); Tue, 1 Nov 2011 15:58:34 -0400 Received: from /spool/local by e5.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 1 Nov 2011 15:58:32 -0400 In-Reply-To: <20111101195111.GA9852@mgebm.net> Sender: linux-arch-owner@vger.kernel.org List-ID: 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 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