From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Buehler Subject: Re: probable vm exit latency issue? Date: Fri, 15 Dec 2017 15:48:02 -0500 Message-ID: <5A343502.8060901@cox.net> References: <5A342458.9010403@cox.net> <5A342F85.9070406@cox.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Konrad Rzeszutek Wilk , kvm@vger.kernel.org To: unlisted-recipients:; (no To-header on input) Return-path: Received: from eastrmfepo201.cox.net ([68.230.241.216]:50689 "EHLO eastrmfepo201.cox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755864AbdLOUsE (ORCPT ); Fri, 15 Dec 2017 15:48:04 -0500 Received: from eastrmimpo305.cox.net ([68.230.241.237]) by eastrmfepo201.cox.net (InterMail vM.8.01.05.28 201-2260-151-171-20160122) with ESMTP id <20171215204804.HUHE4103.eastrmfepo201.cox.net@eastrmimpo305.cox.net> for ; Fri, 15 Dec 2017 15:48:04 -0500 In-Reply-To: <5A342F85.9070406@cox.net> Sender: kvm-owner@vger.kernel.org List-ID: I switched back to virtio for the disk; it has the same issue. It apparently exits the VM via vp_notify(); in the trace I am looking at for almost 8 milliseconds. I had been thinking in terms of disk writes but of course this could be any disk activity so overlayroot will not solve this. It would seem that I might be looking at an inevitable disk rotation latency, which no host tuning will fix. Would a second CPU in the VM solve this or does virtio halt the whole VM for disk I/O? Or perhaps what I really need is to quiesce everything else in the VM to avoid all disk I/O? I suppose I could use a RAM root filesystem -- ugh. I find it a little puzzling that I have not seen disk I/O mentioned much in the realtime KVM literature I have found on the web. Joe Buehler