[U-Boot] [PATCH] sunxi: improve throughput in the sunxi_mmc driver

[Maxime Ripard]

On Wed, Apr 04, 2018 at 12:13:01PM +0530, Jagan Teki wrote:
> On Wed, Mar 21, 2018 at 4:48 PM, Maxime Ripard
> <maxime.ripard at bootlin.com> wrote:
> > From: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> >
> > Throughput tests have shown the sunxi_mmc driver to take over 10s to
> > read 10MB from a fast eMMC device due to excessive delays in polling
> > loops.
> >
> > This commit restructures the main polling loops to use get_timer(...)
> > to determine whether a (millisecond) timeout has expired.  We choose
> > not to use the wait_bit function, as we don't need interruptability
> > with ctrl-c and have at least one case where two bits (one for an
> > error condition and another one for completion) need to be read and
> > using wait_bit would have not added to the clarity.
> >
> > The observed speedup in testing on a A31 is greater than 10x (e.g. a
> > 10MB write decreases from 9.302s to 0.884s).
> 
> Fyi: I've seen significant improvement, but not 10x on A64
> (bananpi-m64) with read
> 
> Before this change:
> 
> => mmc dev 0
> switch to partitions #0, OK
> mmc0 is current device
> => fatload mmc 0:1 $kernel_addr_r Image
> reading Image
> 16310784 bytes read in 821 ms (18.9 MiB/s)
> => mmc dev 1
> switch to partitions #0, OK
> mmc1(part 0) is current device
> => ext4load mmc 1:1 $kernel_addr_r Image
> 16310784 bytes read in 1109 ms (14 MiB/s)
> 
> 
> After this change:
> 
> => mmc dev 0
> switch to partitions #0, OK
> mmc0 is current device
> => fatload mmc 0:1 $kernel_addr_r Image
> 16310784 bytes read in 784 ms (19.8 MiB/s)
> => mmc dev 1
> switch to partitions #0, OK
> mmc1(part 0) is current device
> => ext4load mmc 1:1 $kernel_addr_r Image
> 16310784 bytes read in 793 ms (19.6 MiB/s)

Yeah, the smaller the file is, the bigger the gain is. Since you have
an almost twice bigger file, the gains are probably just noise at that
point and the bottleneck starts to be your MMC.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com
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