From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54454) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fdARL-0003xL-Gs for qemu-devel@nongnu.org; Wed, 11 Jul 2018 04:25:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fdARK-0001NQ-J7 for qemu-devel@nongnu.org; Wed, 11 Jul 2018 04:25:35 -0400 Date: Wed, 11 Jul 2018 10:25:26 +0200 From: Kevin Wolf Message-ID: <20180711082526.GA4266@localhost.localdomain> References: <1531235146-6048-1-git-send-email-pl@kamp.de> <20180710153155.GM5852@localhost.localdomain> <73DCB217-9027-4248-8C81-A83AD4512927@kamp.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <73DCB217-9027-4248-8C81-A83AD4512927@kamp.de> Subject: Re: [Qemu-devel] [PATCH V5] qemu-img: align result of is_allocated_sectors List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Am 10.07.2018 um 22:16 hat Peter Lieven geschrieben: > > > > Am 10.07.2018 um 17:31 schrieb Kevin Wolf : > > > > Am 10.07.2018 um 17:05 hat Peter Lieven geschrieben: > >> We currently don't enforce that the sparse segments we detect during convert are > >> aligned. This leads to unnecessary and costly read-modify-write cycles either > >> internally in Qemu or in the background on the storage device as nearly all > >> modern filesystems or hardware have a 4k alignment internally. > >> > >> This patch modifies is_allocated_sectors so that its *pnum result will always > >> end at an alignment boundary. This way all requests will end at an alignment > >> boundary. The start of all requests will also be aligned as long as the results > >> of get_block_status do not lead to an unaligned offset. > >> > >> The number of RMW cycles when converting an example image [1] to a raw device that > >> has 4k sector size is about 4600 4k read requests to perform a total of about 15000 > >> write requests. With this path the additional 4600 read requests are eliminated while > >> the number of total write requests stays constant. > >> > >> [1] https://cloud-images.ubuntu.com/releases/16.04/release/ubuntu-16.04-server-cloudimg-amd64-disk1.vmdk > >> > >> Signed-off-by: Peter Lieven > > > > It looked convincing, but I'm afraid this is still not correct. > > qemu-iotests 122 fails for me with this patch. > > I will have a look, where and why exactly it fails, but the allocation > pattern might be slightly different due to the alignment. What counts > is that the output is byte identical or not? Right, I noticed only after sending this email that it's qemu-img map output that changes and this might actually be okay. I didn't check, however, if the exact changes are what is expected and whether we need to add more test cases to cover what the test originally wanted to cover. So after all, there's a good chance that all that's missing is just an update to the test case. Kevin