Re: [00/17] Large Blocksize Support V3

From: Pierre Ossman
Date: Sat Apr 28 2007 - 06:55:42 EST

Eric W. Biederman wrote:
> I have a hard time believe that device hardware limits don't allow them
> to have enough space to handle larger requests. If so it was a poor
> design by the hardware manufacturers.

In the MMC layer, the block size is a major bottle neck. None of the currently
supported hardware supports scatter/gather so we're restricted to servicing a
single continuous chunk of memory at a time. And since latency is substantial
for MMC/SD, good performance is several orders above 4k. We get ~8 MB/s for
cards which are supposed to do 20 MB/s (which has been tested against other
systems where we can get larger memory chunks), and the peasants are getting a
bit unruly.

I plan to experiment with some bounce buffer scheme to get performance up, but
getting large blocks directly would make such hacks unnecessary.

Just my two cents.


-- Pierre Ossman

Linux kernel, MMC maintainer
PulseAudio, core developer
rdesktop, core developer
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