[U-Boot] [RFC][PATCH] block: Enable block cache by default

[Marek Vasut]

On 05/20/2018 12:29 AM, Tom Rini wrote:
> On Sat, May 19, 2018 at 11:39:38PM +0200, Marek Vasut wrote:
>> On 05/19/2018 10:50 PM, Tom Rini wrote:
>>> On Sat, May 19, 2018 at 08:20:30PM +0200, Marek Vasut wrote:
>>>> On 05/19/2018 04:36 PM, Simon Glass wrote:
>>>>> On 18 May 2018 at 03:22, Marek Vasut <marex at denx.de> wrote:
>>>>>>
>>>>>> The recent ext4 cache discussion would indicate that the block cache
>>>>>> is a desired feature, yet hidden and not enabled most of the time.
>>>>>> Enable the block cache by default since it provides significant block
>>>>>> device access performance improvement and if there are some users who
>>>>>> cannot enable it ie. due to size limitations, those should disable it
>>>>>> explicitly in their board config.
>>>>>>
>>>>>> Signed-off-by: Marek Vasut <marex at denx.de>
>>>>>> Cc: Simon Glass <sjg at chromium.org>
>>>>>> Cc: Michal Simek <michal.simek at xilinx.com>
>>>>>> Cc: Tom Rini <trini at konsulko.com>
>>>>>> ---
>>>>>>  drivers/block/Kconfig | 2 +-
>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>>>
>>>> I was hoping to get some feedback ?
>>>
>>> So, as I was asking on IRC, can you show the code paths where this gets
>>> used outside of CONFIG_BLK and then really ext4/fat/btrfs as I do in my
>>> patch?
>>
>> Can you summarize that discussion for everyone who was not on IRC at
>> that point ?
> 
> So I posted https://patchwork.ozlabs.org/patch/913266/ and it depends on
> BLK, as without BLK it does compile but isn't useful, but also isn't
> wholly discarded (due to the invalidate call in disk/part.c).

Maybe that is what needs fixing and then this patch can be applied ?

> AFIACT
> from a quick read of the code, block cache is only useful on filesystems
> that reside on block devices.  It won't help with "just" MMC reads for
> example.  So we should only enable it by default in the case of
> filesystems that are usually on block devices being enabled.

I wonder if this not helping with raw block reads is fine or not.
Thoughts ?

> But I didn't dig through the code hard enough to see if it would be
> useful on say UBIFS or if I'm wrong about it not being in the code path
> of things like say NAND.

I don't see why this won't be useful on UBI/UBIFS . It is probably just
not implemented yet.

> But I also don't think just default y in all cases is right as that's
> adding non-trivial mounts of code on all of the platforms that don't /
> won't make use of it.

So it should be discarded if there are no users ?

-- 
Best regards,
Marek Vasut