From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH 3/4] kvm tools: Add debug feature to test the IO thread Date: Tue, 19 Apr 2011 20:04:27 +0300 Message-ID: <1303232667.6697.5.camel@stimpy> References: <1303131754-25072-1-git-send-email-levinsasha928@gmail.com> <1303131754-25072-3-git-send-email-levinsasha928@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: mingo@elte.hu, asias.hejun@gmail.com, gorcunov@gmail.com, prasadjoshi124@gmail.com, kvm@vger.kernel.org To: Pekka Enberg Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:41089 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752529Ab1DSREq (ORCPT ); Tue, 19 Apr 2011 13:04:46 -0400 Received: by wya21 with SMTP id 21so4992981wya.19 for ; Tue, 19 Apr 2011 10:04:45 -0700 (PDT) In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Tue, 2011-04-19 at 19:52 +0300, Pekka Enberg wrote: > On Mon, Apr 18, 2011 at 4:02 PM, Sasha Levin wrote: > > Add --debug-io-delay-cycles and --debug-io-delay-amount to delay the completion of IO requests within virtio-blk. > > This feature allows to verify and debug the threading within virtio-blk. > > > > Signed-off-by: Sasha Levin > > Well, to be honest, I'm not convinced we need both of these. Isn't > --debug-io-delay= enough for our use? This came up during our testing. Ingo suggested a large delay so we could easily see the results of threading. The problem we encountered was that having a delay right from the beginning will make the guest kernel take a rather long time to boot and would make actually testing the threading impossible. I've added a delay before the activation of the I/O request completion delay to give the tester/debugger enough time to boot into the guest and prepare anything needed for the test. Making it a constant is also rather hard because different kernels can take a very different amount of I/O requests to boot. Take the simple example of a whether fsck was running during the boot or not. -- Sasha.