From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update vm irq routing table Date: Thu, 28 Nov 2013 13:23:48 +0200 Message-ID: <20131128112348.GF5822@minantech.com> References: <5294BC3B.6070902@redhat.com> <5297050E.6000700@redhat.com> <20131128091903.GA4609@kernel.org> <5297118C.3050104@cloudius-systems.com> <529712A1.8090207@redhat.com> <5297181B.3090109@cloudius-systems.com> <52971D86.60601@redhat.com> <20131128110915.GD5822@minantech.com> <529724B0.80405@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , "Zhanghaoyu (A)" , Gleb Natapov , Avi Kivity , "Huangweidong (C)" , KVM , "Michael S. Tsirkin" , "Jinxin (F)" , Luonengjun , "qemu-devel@nongnu.org" , Zanghongyong To: Paolo Bonzini Return-path: Received: from mail-wi0-f173.google.com ([209.85.212.173]:58013 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752306Ab3K1LYO (ORCPT ); Thu, 28 Nov 2013 06:24:14 -0500 Received: by mail-wi0-f173.google.com with SMTP id hm4so688615wib.6 for ; Thu, 28 Nov 2013 03:24:10 -0800 (PST) Content-Disposition: inline In-Reply-To: <529724B0.80405@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, Nov 28, 2013 at 12:10:40PM +0100, Paolo Bonzini wrote: > Il 28/11/2013 12:09, Gleb Natapov ha scritto: > > > - if there are no callbacks, but there are readers, synchronize_srcu > > > busy-loops for some time checking if the readers complete. After a > > > while (20 us for synchronize_srcu, 120 us for > > > synchronize_srcu_expedited) it gives up and starts using a workqueue to > > > poll every millisecond. This should never happen unless > > > > Unless what ? :) Unless reader is scheduled out? > > Yes. Or unless my brain is scheduled out in the middle of a sentence. > So we will have to disable preemption in a reader to prevent big latencies for a writer, no? -- Gleb.