From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:57805)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <a175818323@gmail.com>) id 1cCIeL-0004b1-L9
	for qemu-devel@nongnu.org; Wed, 30 Nov 2016 23:07:10 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <a175818323@gmail.com>) id 1cCIeK-0007Gm-Sl
	for qemu-devel@nongnu.org; Wed, 30 Nov 2016 23:07:09 -0500
MIME-Version: 1.0
From: Bob Chen <a175818323@gmail.com>
Date: Thu, 1 Dec 2016 12:07:03 +0800
Message-ID: <CAMxP3BQptSjDJCoakSjT4CU-034rj4hgQ5JoQsoxMCk-3sQpKw@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Subject: [Qemu-devel] QEMU 1.1.2: block IO throttle might occasionally
 freeze running process's IO to zero
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-block@nongnu.org, qemu-devel@nongnu.org

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).