Re: [PATCH] Promise 'stex' driver

From: Jens Axboe
Date: Thu Jul 20 2006 - 21:36:32 EST

On Thu, Jul 20 2006, Jeff Garzik wrote:
> Jens Axboe wrote:
> >On Thu, Jul 20 2006, Jeff Garzik wrote:
> >>James Bottomley wrote:
> >>>On Thu, 2006-07-20 at 17:27 -0400, Jeff Garzik wrote:
> >>>>Since _no individual SCSI driver_ uses the block layer
> >>>>tagging, it is likely that some instability and core kernel
> >>>>development
> >>>>will occur, in order to make that work.
> >>>That's not quite true: 53c700 and tmscsim both use it ... I could with
> >>>the usage were wider, but at least 53c700 has pretty regular and
> >>>constant usage ... enough I think to validate the block tag code (it's
> >>>been using it for the last three years).
> >>Not for the case being discussed in this thread, adapter-wide tags.
> >
> >That just means the map is shared, otherwise there should be little if
> >any difference.
> >
> >>AFAICS, no file in include/scsi/* or drivers/scsi/* ever calls
> >>blk_queue_init_tags() with a non-NULL third arg.
> >
> >grpe again, it's in scsi_tcq.h.
> What tree are you looking at?
> There is only one user in the entire tree, and NULL is hardcoded as the
> third arg. This is 2.6.18-rc2:

Sorry, missed your non-NULL statement, I thought you meant in generel.

As long as you get the locking right for the map access, there's really
nothing that seperates shared vs non-shared tag mappings. So I don't
think it's a big deal.

If we don't encourage new drivers to use the block layer tagging, we
might as well not bother with it.

Jens Axboe

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