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dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AS8PR08MB6038.eurprd08.prod.outlook.com (2603:10a6:20b:23f::24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3846.27; Fri, 12 Feb 2021 11:34:14 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::f1f0:6610:11f5:5e4a]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::f1f0:6610:11f5:5e4a%9]) with mapi id 15.20.3846.034; Fri, 12 Feb 2021 11:34:14 +0000 Subject: Re: [PATCH v2 1/2] block: Explicit null-co uses 'read-zeroes=false' To: Eric Blake , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org Cc: Fam Zheng , Laurent Vivier , Thomas Huth , qemu-block@nongnu.org, Markus Armbruster , Wainer dos Santos Moschetta , Max Reitz , Alexander Bulekov , Bandan Das , Stefan Hajnoczi , Cleber Rosa , Paolo Bonzini , Kevin Wolf References: <20210211142656.3818078-1-philmd@redhat.com> <20210211142656.3818078-2-philmd@redhat.com> <40f42cc8-521f-5090-63cf-b4549be43905@redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: Date: Fri, 12 Feb 2021 14:34:12 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR04-HE1-obe.outbound.protection.outlook.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.119, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 12.02.2021 01:40, Eric Blake wrote: > On 2/11/21 8:26 AM, Philippe Mathieu-Daudé wrote: >> We are going to switch the 'null-co' default 'read-zeroes' value >> from FALSE to TRUE in the next commit. First explicit the FALSE >> value when it is not set. > > Grammar suggestion, along with a suggestion for an additional sentence > to make the intent of this commit clearer: > > As a first step, request an explicit FALSE value rather than relying on > the defaults. This is intended to be a purely mechanical adjustment for > no performance behavior in the tests; later patches may then flip or > elide the explicit choice for tests where performance does not matter. > >> >> Suggested-by: Eric Blake >> Signed-off-by: Philippe Mathieu-Daudé >> --- >> - Missing: 056 & 155. I couldn't figure out the proper syntax, >> any help welcomed... > > 056 - looks like just one line: > self.vm = > iotests.VM().add_drive_raw("file=blkdebug::null-co://,id=drive0,align=65536,driver=blkdebug") > > the best way to add it here would be rewriting that line to use blockdev > syntax rather than blkdebug: URI syntax. The other question is whether > it is a noticeable time difference when the default is flipped in 2/2. > > 155 - looks like several uses such as: > > class TestBlockdevMirrorForcedBacking(MirrorBaseClass): > cmd = 'blockdev-mirror' > existing = True > target_backing = None > target_blockdev_backing = { 'driver': 'null-co' } > target_real_backing = 'null-co://' > > >> - I'm unsure about 162, this doesn't seem to use the null-co >> driver but rather testing global syntax. > > Concur; I don't see any reason to worry about this one (but mentioning > it in the commit message can't hurt in case someone asks later) > > # blkdebug expects all of its arguments to be strings, but its > # bdrv_refresh_filename() implementation should not assume that they > have been > # passed as strings in the original options QDict. > # So this should emit blkdebug:42:null-co:// as the filename: > touch 42 > $QEMU_IMG info 'json:{"driver": "blkdebug", "config": 42, > "image.driver": "null-co"}' \ > > >> --- >> docs/devel/testing.rst | 14 +++++++------- >> tests/qtest/fuzz/generic_fuzz_configs.h | 11 ++++++----- >> tests/test-bdrv-drain.c | 10 ++++++++-- >> tests/acceptance/virtio_check_params.py | 2 +- >> tests/perf/block/qcow2/convert-blockstatus | 6 +++--- >> tests/qemu-iotests/040 | 2 +- > > You did a pretty good hunt for culprits! > >> tests/qemu-iotests/041 | 12 ++++++++---- >> tests/qemu-iotests/051 | 2 +- >> tests/qemu-iotests/051.out | 2 +- >> tests/qemu-iotests/051.pc.out | 4 ++-- > > and for the fallout to the iotests. > > I did not audit for which tests are easy candidates for dropping the > explicit read-zeroes=false (that is, where the extra time in allowing > the flipped default doesn't penalize the test), but am okay giving this > patch: > > Reviewed-by: Eric Blake > > I'd keep tests/qemu-iotests as is.. Benefits of keeping old behavior (by adding read-zeroes=false) - saving several milliseconds. I doubt that it would be even noticeable. Could you give have much time of "make check-block" it saves, if we update all iotests to use read-zeroes=false, instead of transparently move to new default? Drawbacks of adding read-zeroes=false: - it's generally better to test only default behavior than only non-default behavior - this patch creates extra conflicts on any patch porting between upstream/downstream - for new tests, nobady will care about read-zeroes and will not add it.. (or will add when copy existing test no thinking about it), so it will be a kind of mess -- Best regards, Vladimir