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Wed, 9 Mar 2022 14:42:52 +0000 (GMT) Received: from [192.168.8.130] (106.210.248.212) by CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Wed, 9 Mar 2022 14:42:46 +0000 Message-ID: Date: Wed, 9 Mar 2022 15:42:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH 6/6] null_blk: Add support for power_of_2 emulation to the null blk device Content-Language: en-US To: Damien Le Moal , Luis Chamberlain , Adam Manzanares , =?UTF-8?Q?Javier_Gonz=c3=a1lez?= , kanchan Joshi , Jens Axboe , Keith Busch , Christoph Hellwig , Sagi Grimberg , =?UTF-8?Q?Matias_Bj=c3=b8rling?= , CC: Pankaj Raghav , Kanchan Joshi , , From: Pankaj Raghav In-Reply-To: <91d1f4c8-946d-c6b2-d30e-f9af4424221f@opensource.wdc.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [106.210.248.212] X-ClientProxiedBy: CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) To CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrPKsWRmVeSWpSXmKPExsWy7djPc7pv9mgkGTTdUbFYfbefzeL32fPM FitXH2Wy6DnwgcXi/NvDTBaTDl1jtNh7S9ti/rKn7BYT2r4yW9yY8JTRYs3NpywW616/Z3Hg 8fh3Yg2bx85Zd9k9zt/byOJx+Wypx6ZVnWwem5fUe+y+2QCUa73P6vF5k5xH+4FupgCuKC6b lNSczLLUIn27BK6M6e+uMhes5K9oPHuOqYGxnaeLkZNDQsBE4tT6lexdjFwcQgIrGCXmXtoD 5XxhlPhw7w8ThPOZUeLZ1qPMMC0nfz1gA7GFBJYzSnSuyIEretH5mBXC2cUocWzlcyaQKl4B O4kNS26zgNgsAioS2w/OYoGIC0qcnPkEzBYViJB4eeQvWL2wQIJE+8VJYBuYBcQlbj2ZD3aG iMA5ZomLHZNZIRITgVbvMu9i5OBgE9CSaOxkBwlzCrhJNB9eCdWrKdG6/Tc7hC0vsf3tHGaQ cgkBZYnX620gnqmVWHvsDNjLEgLnOCXeT9nKCJFwkbi+4xoLhC0s8er4FnYIW0bi/06IeyQE +hklprb8gXJmMEr0HN7MBLHBWqLvTA5Eg6PEsQNHocJ8EjfeCkLcwycxadt05gmMqrOQgmIW kpdnIXlhFpIXFjCyrGIUTy0tzk1PLTbKSy3XK07MLS7NS9dLzs/dxAhMc6f/Hf+yg3H5q496 hxiZOBgPMUpwMCuJ8DaFaiQJ8aYkVlalFuXHF5XmpBYfYpTmYFES503O3JAoJJCeWJKanZpa kFoEk2Xi4JRqYKpeu3j9++SDK48Z2LPKVYgcil1le62V9eafh9Kc+/p04nZ4ZNkzy+vuay9T 9v5pw3nbWzhLt0msV0n/tFWU4/6brqek/4dc2yPZzZKwJH8Lr8BNrse1z90WvH6/r07j5b+M nT6nZ3QfviF3117+1Vkx0YfLFQPdr27ULk5ZsfZKuNXvuRP/Ptq/ekalukP9vUt/rU7tfne6 a+J0qw8rvla88P6yxKzdhk01cU1rrmWAwkOhx3lr2SPPzubIPfdZbdGb6IrT2y7a8E7N6Zyw NMXk7o7O7DXbv6xo8f//fHn8jh2rD3mvapbYkLBBLmunkVHQq1+853J/nLj57UVEmJdkkNOB Zs51DJKuK9gyd3gosRRnJBpqMRcVJwIAbs5+h+IDAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFmplleLIzCtJLcpLzFFi42I5/e/4Xd03ezSSDOafY7NYfbefzeL32fPM FitXH2Wy6DnwgcXi/NvDTBaTDl1jtNh7S9ti/rKn7BYT2r4yW9yY8JTRYs3NpywW616/Z3Hg 8fh3Yg2bx85Zd9k9zt/byOJx+Wypx6ZVnWwem5fUe+y+2QCUa73P6vF5k5xH+4FupgCuKD2b ovzSklSFjPziElulaEMLIz1DSws9IxNLPUNj81grI1MlfTublNSczLLUIn27BL2M6e+uMhes 5K9oPHuOqYGxnaeLkZNDQsBE4uSvB2xdjFwcQgJLGSWuPLjJDpGQkfh05SOULSzx51oXVNFH RolNK05DObsYJV7Pec4IUsUrYCexYcltFhCbRUBFYvvBWSwQcUGJkzOfgNmiAhESbcumMIPY wgIJEjdefmcCsZkFxCVuPZnPBDJUROAcs8TFjsmsIA6zQD+jxJIpP1gh1v1mlFj6YhGQw8HB JqAl0dgJdh+ngJtE8+GVbBCTNCVat/9mh7DlJba/ncMMUi4hoCzxer0NxDu1Eq/u72acwCg6 C8l9s5DcMQvJpFlIJi1gZFnFKJJaWpybnltspFecmFtcmpeul5yfu4kRmB62Hfu5ZQfjylcf 9Q4xMnEwHmKU4GBWEuFtCtVIEuJNSaysSi3Kjy8qzUktPsRoCgykicxSosn5wASVVxJvaGZg amhiZmlgamlmrCTO61nQkSgkkJ5YkpqdmlqQWgTTx8TBKdXApBkUEXT/HcPXuqPbXs1+fTKU 6Rzbbs91cRarjs26VM0q45sscOJ7lPHPBfoS0Sumq/kzOc1dOcfwieonbpXs3omSaewL1hwV mCWVvfyu1xeRee4Pb+h1aC2b8vgrZ9kxn8nz3K/eid/04fy555qC/AG2u646GkyLmL0jddL+ 1Ya3eph6WHassEnYsfHiE85Fs/OZHrBleMxI2PnSJyvSzCHsuKtQS4jiSYWT6841/OITvJG6 KWia3a7ttZ4TK67pv/giapJeur7iRX6tPsP6aMtZq+IvRrSV5O19Jn874fGKPBXWXNMzL5d4 2mleeu7whTtAIYvBw/Mi80e+L7KfSrkbFj4sn3HvU/I11aeTVyuxFGckGmoxFxUnAgC5iPvd mAMAAA== X-CMS-MailID: 20220309144252eucas1p124afc2916b9f5845830d2e0c0893b1ad X-Msg-Generator: CA X-RootMTR: 20220308165448eucas1p12c7c302a4b239db64b49d54cc3c1f0ac X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20220308165448eucas1p12c7c302a4b239db64b49d54cc3c1f0ac References: <20220308165349.231320-1-p.raghav@samsung.com> <20220308165349.231320-7-p.raghav@samsung.com> <91d1f4c8-946d-c6b2-d30e-f9af4424221f@opensource.wdc.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220309_064255_526285_0C05DDB3 X-CRM114-Status: GOOD ( 27.58 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 2022-03-09 05:09, Damien Le Moal wrote: > On 3/9/22 01:53, Pankaj Raghav wrote: >> power_of_2(PO2) emulation support is added to the null blk device to >> measure performance. >> >> Callbacks are added in the hotpaths that require PO2 emulation specific >> behaviour to reduce the impact on exisiting path. >> >> The power_of_2 emulation support is wired up for both the request and >> the bio queue mode and it is automatically enabled when the given zone >> size is non-power_of_2. > > This does not make any sense. Why would you want to add power of 2 zone > size emulation to nullblk ? Just set the zone size to be a power of 2... > > If this is for test purpose, then use QEMU. These changes make no sense > to me here. > I see your point but this was mainly added to measure the performance impact. I ran the conformance test with different configurations in QEMU but I don't think QEMU would be a preferred option to measure performance, especially, if we want to account for changes we did to the hot path with a indirection. As ZNS drives are not available in retail stores, this patch also provides a way for the community to reproduce the performance analysis that we did without needing a real device. > A change that would make sense in the context of this series is to allow > for setting a zoned null_blk device zone size to a non power of 2 size. This is not possible with the block layer expecting the zone sizes to be po2. A null blk device with non po2 zone size will only work with the emulation that is added as a part of this patch. As I said before, once we relax the block layer requirement, then we could allow non po2 zone sizes without a lot of changes to the null blk device. > But this series does not actually deal with that. So do not touch this > driver please. > If you really think it doesn't belong here, then I can take it out in the next revision. -- Regards, Pankaj