From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v3 1/3] Introduce a workqueue to deliver PIT timer interrupts. Date: Mon, 16 Apr 2012 18:33:26 +0200 Message-ID: <4F8C49D6.9010603@siemens.com> References: <1276722673-19011-1-git-send-email-clalance@redhat.com> <1276722673-19011-2-git-send-email-clalance@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Marcelo Tosatti , Avi Kivity , Gleb Natapov To: Chris Lalancette Return-path: Received: from david.siemens.de ([192.35.17.14]:26922 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753311Ab2DPQdb (ORCPT ); Mon, 16 Apr 2012 12:33:31 -0400 In-Reply-To: <1276722673-19011-2-git-send-email-clalance@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2010-06-16 23:11, Chris Lalancette wrote: > We really want to "kvm_set_irq" during the hrtimer callback, > but that is risky because that is during interrupt context. > Instead, offload the work to a workqueue, which is a bit safer > and should provide most of the same functionality. Unfortunately, workqueues do not have fixed kthread associations (and "kvm-pit-wq" would be too unspecific when running multiple VMs). So I just realized that this subtly breaks the ability to run KVM guests with RT priority (boot managers with timeouts hang as the workqueue starves). Before throwing some kthread_worker at this, could someone help me recalling what was "risky" here? That the PIT IRQ may have to be broadcast to a large number of VCPUs? I would offer to include this information in my changelog. ;) Thanks, Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux