linux-kernel - Re: [RFC/PATCH 1/1] ubi: Add ubiblock driver

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Message-ID: <CALF0-+UVNwAcEe5UVK9MdKYGwwubCi70DRXdWaojEUDg3uR+Xg@mail.gmail.com>
Date:	Wed, 21 Nov 2012 07:20:30 -0300
From:	Ezequiel Garcia <elezegarcia@...il.com>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	michael.opdenacker@...e-electrons.com, dwmw2@...radead.org,
	Tim Bird <tim.bird@...sony.com>,
	Artem Bityutskiy <dedekind1@...il.com>
Subject: Re: [RFC/PATCH 1/1] ubi: Add ubiblock driver

On Tue, Nov 20, 2012 at 8:59 PM, richard -rw- weinberger
<richard.weinberger@...il.com> wrote:
> On Tue, Nov 20, 2012 at 11:39 PM, Ezequiel Garcia <elezegarcia@...il.com> wrote:
>> Block device emulation on top of ubi volumes with read/write support.
>> Block devices get automatically created for each ubi volume present.
>>
>> Each ubiblock is fairly cheap since it's based on workqueues
>> and not on threads.
>>
>> Read/write access is expected to work fairly well because the
>> request queue at block elevator orders block transfers to be space-effective.
>> In other words, it's expected that reads and writes gets ordered
>> to point to the same LEB.
>>
>> To help this and reduce access to the UBI volume, a 1-LEB size
>> write-back cache has been implemented.
>> Every read and every write, goes through this cache and the write is
>> only done when a request arrives to read or write to a different LEB
>> or when the device is released, when the last file handle is closed.
>
> Did you also benchmark your driver with two caches?
> (One for reading and one for writing.)
> By using two caches you can lower the amount of atomic LEB changes.
>
> Maybe it would be also good to ensure that an cache entry becomes not too old.
>

Yes, I thought of this.

For now, I decided to keep the implementation as simple as possible.

Regards,

    Ezequiel
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