From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46329) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XlLvQ-0005zl-26 for qemu-devel@nongnu.org; Mon, 03 Nov 2014 13:00:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XlLvJ-0002Lx-Qt for qemu-devel@nongnu.org; Mon, 03 Nov 2014 13:00:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49558) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XlLvJ-0002Ll-EX for qemu-devel@nongnu.org; Mon, 03 Nov 2014 13:00:13 -0500 Message-ID: <5457B62C.1000605@redhat.com> Date: Mon, 03 Nov 2014 18:06:52 +0100 From: Max Reitz MIME-Version: 1.0 References: <1415034271-8774-1-git-send-email-mreitz@redhat.com> In-Reply-To: <1415034271-8774-1-git-send-email-mreitz@redhat.com> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 00/12] qcow2: Add new overlap check functions List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Kevin Wolf , Peter Lieven , =?ISO-8859-15?Q?Beno=EEt_Canet?= , Stefan Hajnoczi On 2014-11-03 at 18:04, Max Reitz wrote: > As has been requested, this series adds new overlap check functions to > the qcow2 code. My local branch is called "qcow2-improved-overlap-v1", > but I am not so sure whether it is actually an improvement; that is lef= t > for you to decide, dear reviewers. > > See patch 1 for an explanation of why this series exists and what it > does. Patch 1 is basically the core of this series, the rest just > employs the functions introduced there. > > I have yet to do benchmarks to test whether this series actually > improves things, but judging from the iotests it at least does not slow > things down (which it did at one time during development, particularily > test 044 is good for testing this, so this actually has some > significance to it). > > In a later patch, we may want to change the meaning of the "constant" > overlap checking option to mean the same as "cached", which is > everything except for inactive L2 tables. This series does make > checking for overlaps with inactive L2 tables at runtime just as cheap > as everything else (constant time plus caching), but using these checks > means qemu has to read all the snapshot L1 tables when opening a qcow2 > file. This does not take long, of course, but it does result in a bit o= f > overhead so I did not want to enable it by default. > > I think just enabling all overlap checks by default after this series > should be fine and useful, though. Sorry Beno=EEt, I mistyped your address. Maybe I should learn how to use=20 abbreviations with git send-email some time... Max