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

[Maxime Ripard]

Hi,

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.
> TX_TRANSACTION_SIZE and RX_TRANSACTION_SIZE) from default 0x0 each
> 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
>   and http://linux-sunxi.org/SATA#Devices_with_SATA_ports
>   See also http://linux-sunxi.org/Category:Devices_with_SATA_port
>
> 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:
>     http://lkml.iu.edu/hypermail/linux/kernel/1905.1/03506.html
>   - Posted a dd test script to find optimal bs, and some results:
>     https://bit.ly/2YoOzEM
>
> 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.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com