lkml.org 
[lkml]   [2019]   [Jan]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: remove block layer bounce buffering for MMC
On Mon, Jan 14, 2019 at 11:27 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> +Linus Walleij (recently made a cleanup of the mmc bounce buffering code).
>
> On Mon, 14 Jan 2019 at 10:58, Christoph Hellwig <hch@lst.de> 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

\
 
 \ /
  Last update: 2019-01-16 11:25    [W:0.337 / U:0.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site