Re: [Xen-devel] bug when using 4K sectors?

[Joseph Glanville <joseph.glanville@xxxxxxxxxxxxxx>]

On 16 September 2012 18:31, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
> On 16/09/2012 08:00, "Joseph Glanville" <joseph.glanville@xxxxxxxxxxxxxx>
> wrote:
>
>> After reading through blkback it appears that it can only support 512
>> byte sector sizes and removing this limitation would take quite abit
>> of work.
>> It uses hard coded bitshifts pervasively to convert between number of
>> requests/pages and size of sectors etc. (that is all the >> 9
>> everywhere)
>>
>> I am going to see what I can about working on getting it to support 4k
>> sectors too and eventually uncoupled logical/physical sizes but that
>> would take even more work as far as I can tell.
>>
>> Being able to use 4k sectors seems like it would provide pretty
>> massive gains in performance just by being more efficient let alone
>> increasing byte aligned writes to the underlying block storage system.
>
> The PV blk transport may be based on 512-byte sectors, but the real sector
> size is communicated between blkfront and blkback via xenbus (field
> 'sector-size') and blkfront is expected to only make requests that are
> multiple of, and aligned according to, that real 'sector-size'.
>
> I would kind of expect it to work, as CD-ROMs have a larger sector size (2kB
> IIRC) and we support those...
>
> Bashing your head against the PV blk transport code may be premature. ;)
>
>  -- Keir
>
>

Understood, still have a fair bit of reading to do. :)

Thanks,
Joseph.

-- 
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