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Wed, 16 Jan 2019 02:25:00 -0800 (PST) MIME-Version: 1.0 References: <20190114095804.27978-1-hch@lst.de> In-Reply-To: From: Arnd Bergmann Date: Wed, 16 Jan 2019 11:24:43 +0100 Message-ID: Subject: Re: remove block layer bounce buffering for MMC To: Ulf Hansson X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190116_022501_809426_9ACE6E8C X-CRM114-Status: GOOD ( 17.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Aaro Koskinen , Linus Walleij , Nicolas Pitre , "linux-mmc@vger.kernel.org" , Russell King , Linux Kernel Mailing List , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " , Ben Dooks , linux-omap , Christoph Hellwig , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jan 14, 2019 at 11:27 AM Ulf Hansson wrote: > > +Linus Walleij (recently made a cleanup of the mmc bounce buffering code). > > On Mon, 14 Jan 2019 at 10:58, Christoph Hellwig wrote: > > > > Hi everyone, > > > > this series converts the remaining MMC host drivers to properly kmap the > > scatterlist entries it does PIO operations on, and then goes on to > > remove the usage of block layer bounce buffering (which I plan to remove > > eventually) from the MMC layer. > > > > As a bonus I've converted various drivers to the proper scatterlist > > helpers so that at least in theory they are ready for chained > > scatterlists. > > > > All the changes are compile tested only as I don't have any of the > > hardware, so a careful review would be appreciated. > > Thanks for posting this. I will have a look as soon as I can, but > first needs to catch up with things since the holidays. Linus probably knows more here, but I have a vague recollection of the MMC bounce buffer code being needed mostly for performance reasons: when the scatterlist is discontiguous, that can result in a request being split up into separate MMC commands, which due to the lack of queued commands combined with the need for garbage collection on sub-page writes results in a huge slowdown compared to having larger bounce buffers all the time. We had discussed finding a different way to do this (separate from the bounce buffering), but I don't know if that ever happened, or if this is even the code that you are changing here. Arnd _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel