RE: Poor write performance to boot area using rcar-gen3-sdhi

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-----Original Message-----
From: Richard Weinberger <richard@xxxxxx> 
Sent: Tuesday, May 9, 2023 1:28 PM
To: Christian Loehle <CLoehle@xxxxxxxxxxxxxx>
Cc: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>; linux-mmc <linux-mmc@xxxxxxxxxxxxxxx>; linux-renesas-soc <linux-renesas-soc@xxxxxxxxxxxxxxx>; wsa+renesas <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>; ulf hansson <ulf.hansson@xxxxxxxxxx>
Subject: Re: Poor write performance to boot area using rcar-gen3-sdhi


> So I went down the rabbit hole.
> After analyzing the operation traces from Linux and u-boot in more detail I had another chat with the vendor. It turned out their boot area *is* different, it operates on a much larger internal block size.
> 
> While u-boot does basically all IO with one op code, Linux's writeback via page cache writes 4k wise which leads to catastrophic performance.
> Using O_DIRECT mitigates the issue, though.

Interesting, without having tried it out I would expect the 4k writebacks to be merged to a bigger IO, too? Given that they are filled sequentially, which is the case.
But good that you got it working. 
If I find the time I will play with it a bit.

> 
> Thanks everyone for your valuable input!
> //richard
>

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