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

[Christian Loehle <CLoehle@hyperstone.com>]

> Can it be that rcar-gen3-sdhi changes some timings after switching?
> Either in software or on hardware.

Neither should be aware of the notion of a boot or user area partition.
Anything below mmc/core isn't, if we exclude the boot operation which is read only, so not applicable to your problem.
So also a
while true; do dd if=/dev/zero of=/dev/mmcblkXboot0 bs=128K status=progress; done
gives you like ~50KB/s consistently?


-----Original Message-----
From: Richard Weinberger <richard@nod.at> 
Sent: Tuesday, April 18, 2023 10:11 AM
To: Christian Loehle <CLoehle@hyperstone.com>
Cc: Biju Das <biju.das.jz@bp.renesas.com>; linux-mmc <linux-mmc@vger.kernel.org>; linux-renesas-soc <linux-renesas-soc@vger.kernel.org>; wsa+renesas <wsa+renesas@sang-engineering.com>; ulf hansson <ulf.hansson@linaro.org>
Subject: Re: Poor write performance to boot area using rcar-gen3-sdhi

----- Ursprüngliche Mail -----
> Von: "Christian Loehle" <CLoehle@hyperstone.com> Your eMMC likely 
> treats the boot partitions differently than the user area, e.g.
> in regards to cache.
> Is this reproducible for more 4k writes? What about larger writes?

Yes. So far every write size I tried is slow.
Sometimes (1 out of 50) small writes are fast, that's most likely a caching effect of eMMC internals.

> The eMMC might not even have the mapping available after boot and 
> first has to internally switch to it, in contrast to at u-boot stage?

Wouldn't that explain only the first slow write?
I see poor write speed also on repeated runs.
 
> Anyway this is probably more a question to your eMMC manufacturer and 
> nothing the host is to be blamed, as you mentioned yourself, the time 
> is spent at CMD25.

The eMMC manufacturer says there is nothing special about the boot area and write speed should be equally fast.

Can it be that rcar-gen3-sdhi changes some timings after switching?
Either in software or on hardware.

Thanks,
//richard

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