Re: LSF Papers online?

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2009-04-14 at 19:39 -0600, Robert Hancock wrote:
> James Bottomley wrote:
> > 
> > On a final note about the urgency of getting libata out of SCSI: Intel
> > has been worrying for a while about the fatness of the SCSI/libata
> > stack, and its effects on performance, especially command transmission
> > via SAT, so I'm hoping they'll be supporting the effort.
> 
> I really don't see this as being a big driver for this move. If you look 
> at the code that does the translation of SCSI commands to ATA commands, 
> there really is not much there at all of any consequence to CPU usage. 
> Compared to any kind of hardware/controller interactions I wouldn't say 
> it's likely to be a significant bottleneck at all. In oprofile runs I've 
> done with heavy ATA activity, the top time consumers are the interrupt 
> handlers, command issue paths, code that actually is poking IO 
> registers. The libata-scsi code hasn't even shown up on the radar in my 
> experience.

Been there, said that and got the nicely embroidered polo shirt to prove
it.

The point is, it doesn't really matter what I say or believe, it matters
what they do ... and they believe fat stacks impede the performance of
their SSDs.

James