lkml.org 
[lkml]   [2009]   [Apr]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Implementing NVMHCI...
Jeff Garzik wrote:
> Speaking of RMW... in one sense, we have to deal with RMW anyway.
> Upcoming ATA hard drives will be configured with a normal 512b sector
> API interface, but underlying physical sector size is 1k or 4k.
>
> The disk performs the RMW for us, but we must be aware of physical
> sector size in order to determine proper alignment of on-disk data, to
> minimize RMW cycles.
>

Virtualization has the same issue. OS installers will typically setup
the first partition at sector 63, and that means every page-sized block
access will be misaligned. Particularly bad when the guest's disk is
backed on a regular file.

Windows 2008 aligns partitions on a 1MB boundary, IIRC.

> At the moment, it seems like most of the effort to get these ATA
> devices to perform efficiently is in getting partition / RAID stripe
> offsets set up properly.
>
> So perhaps for NVMHCI we could
> (a) hardcode NVM sector size maximum at 4k
> (b) do RMW in the driver for sector size >4k, and

Why not do it in the block layer? That way it isn't limited to one driver.

> (c) export information indicating the true sector size, in a manner
> similar to how the ATA driver passes that info to userland
> partitioning tools.

Eventually we'll want to allow filesystems to make use of the native
sector size.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.



\
 
 \ /
  Last update: 2009-04-14 12:45    [W:0.419 / U:0.684 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site