Re: [RFC PATCH v2 RESEND] drivers: ata: ahci_sunxi: Increased SATA/AHCI DMA TX/RX FIFOs

From: U.Mutlu
Date: Mon May 13 2019 - 07:22:29 EST

Maxime Ripard wrote on 05/13/2019 11:59 AM:
On Sun, May 12, 2019 at 10:59:54PM +0200, Uenal Mutlu wrote:
Increasing the SATA/AHCI DMA TX/RX FIFOs (P0DMACR.TXTS and .RXTS, ie.
to 0x3 each, gives a write performance boost of 120 MiB/s to 132 MiB/s
from lame 36 MiB/s to 45 MiB/s previously.
Read performance is about 200 MiB/s.
[tested on SSD using dd bs=2K/4K/8K/12K/16K/24K/32K: peak-perf at 12K].

Tested on the Banana Pi R1 (aka Lamobo R1) and Banana Pi M1 SBCs
with Allwinner A20 32bit-SoCs (ARMv7-a / arm-linux-gnueabihf).
These devices are RaspberryPi-like small devices.

This problem of slow SATA write-speed with these small devices lasts now
for more than 5 years. Many commentators throughout the years wrongly
assumed the slow write speed was a hardware limitation. This patch finally
solves the problem, which in fact was just a hard-to-fix software problem
(b/c of lack of documentation by the SoC-maker Allwinner Technology).

RFC: Since more than about 25 similar SBC/SoC models do use the
ahci_sunxi driver, users are encouraged to test it on all the
affected boards and give feedback.

Lists of the affected sunxi and other boards and SoCs with SATA using
the ahci_sunxi driver:
$ grep -i -e "^&ahci" arch/arm/boot/dts/sun*dts
See also

Patch v2:
- Commented the patch in-place in ahci_sunxi.c
- With bs=12K and no conv=... passed to dd, the write performance
rises further to 132 MiB/s
- Changed MB/s to MiB/s
- Posted the story behind the patch:
- Posted a dd test script to find optimal bs, and some results:

Patch v1:
- States bs=4K for dd and a write performance of 120 MiB/s

Signed-off-by: Uenal Mutlu <um@xxxxxxxxxxx>

Acked-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>


Just a minor nitpick though, the part starting with RFC: and with the
version changelog should be after the --- below so that it doesn't get
applied as part of the commit log.

Ok, I'll do it better in the future.
Thx again.


Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering