Re: [patch] qla1280 update for 2.6.1-mm4

[Jes Sorensen <jes@wildopensource.com>]

>>>>> "James" == James Bottomley <James.Bottomley@steeleye.com> writes:

James> Something to think about (I'm not asking you to change it) is
James> whether you really want to use 64 bit descriptors on all 64 bit
James> machines.  The way the qla1280 single issue queue is organised
James> it looks like we eat up slots (and, worse, overflow slots)
James> quite a bit faster in 64 bit addressing mode.  Therefore, it
James> seems like the driver would operate more efficiently in 32 bit
James> mode, so it might be worth a runtime check even on 64 bit
James> machines to see whether the addressing mode is really necessary
James> (i.e. no physical memory > 4GB for instance).

Hi James,

Certainly a valid concern, however it would probably more likely be
based on available IOMMU slots, ie. with loads of 1280's in a box or
other devices causing a lot of packets going through the system, it
will probably be preferred to use 64 bit addressing where on smaller
boxes I think you suggestion will be a pretty decent win. The driver
also needs to handle it's busy situation a lot better, the current
busy wait loop in qla1280_req_pkt is ehm ... no comment. Even if we
decide to do dynamic switching between 64 and 32 bit mappings then I
think it will be desirable to merge the two queuecommand versions for
cache locality.

Cheers,
Jes