On Wed, Jan 16, 2019 at 11:25 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Mon, Jan 14, 2019 at 11:27 AM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > > > > +Linus Walleij (recently made a cleanup of the mmc bounce buffering code). Nah it's not THAT bounce buffer. > 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. Nope not the same code. The term "bounce buffer" is sadly used as ambigously as __underscores in front of function names. That other "bounce buffer" was first deleted and then reimplemented as a local hack in the SDHCI driver core after it caused performance regressions on the i.MX and some laptops, see commit: commit bd9b902798ab14d19ca116b10bde581ddff8f905 mmc: sdhci: Implement an SDHCI-specific bounce buffer That should be orthogonal to Christoph's changes in this patch series. Yours, Linus Walleij
