From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36356) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cCOR3-0000ZF-Bq for qemu-devel@nongnu.org; Thu, 01 Dec 2016 05:17:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cCOR2-0008B3-GN for qemu-devel@nongnu.org; Thu, 01 Dec 2016 05:17:49 -0500 Sender: Paolo Bonzini References: From: Paolo Bonzini Message-ID: Date: Thu, 1 Dec 2016 11:16:28 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally freeze running process's IO to zero List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Bob Chen , qemu-devel , qemu block On 01/12/2016 05:07, Bob Chen wrote: > Test case: > > 1. QEMU 1.1.2 > 2. Run fio inside the vm, give it some pressure. Watch the realtime > throughput > 3. block_set_io_throttle drive_2 100000000 0 0 2000 0 0 # > throttle bps and iops, any value > 4. Observed that the IO is very likely to freeze to zero. The fio > process stuck! > 5. Kill the former fio process, start a new one. The IO turns back to normal > > Didn't reproduce it with QEMU 2.5. > > > Actually I'm not wishfully thinking the community would help fix this > bug on such an ancient version. Just hope someone can tell me what is > the root cause. Then I have to evaluate whether I should move to higher > version QEMU, or fix this bug on 1.1.2 in-place(if it is a small one). Hi, throttling has been rewritten in QEMU 2.0 (see the commits around 5ddfffb, "throttle: Add a new throttling API implementing continuous leaky bucket.", 2013-09-06), so the root cause is simply that the old algorithms were buggy. :) I think that the new implementation has been backported to QEMU versions as old as 1.1.2, but if you can move to a newer version it would be simpler. Paolo