Re: Any objections/comments on axing out old ATA stack?

Am 27.03.2013 22:22, schrieb Alexander Motin:
> Hi.
> 
> Since FreeBSD 9.0 we are successfully running on the new CAM-based ATA
> stack, using only some controller drivers of old ata(4) by having
> `options ATA_CAM` enabled in all kernels by default. I have a wish to
> drop non-ATA_CAM ata(4) code, unused since that time from the head
> branch to allow further ATA code cleanup.
> 
> Does any one here still uses legacy ATA stack (kernel explicitly built
> without `options ATA_CAM`) for some reason, for example as workaround
> for some regression? Does anybody have good ideas why we should not drop
> it now?

Alexander,

The regression in http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/157397
where the SATA NCQ slots stall for some Samsung drives in the new stack,
and consequently hang the computer for prolonged episodes where it is in
the NCQ error handling, disallows removal of the old driver. (Last
checked with 9.1-RELEASE at current patchlevel.)

Chances are that limiting the open queue slots to 31 might help, but
that is hearsay from what Linux would be doing.

Unless we get a fix, if you want to drop the old driver, you'll need to
add features so that

1. the new driver to lets users (down-)configure the max. number of
tagged openings

2. the new driver allows disabling NCQ altogether for individual drives

3. list the relevant Samsung drives in some quirks data base so that we
avoid the stalls while permitting users to "open it up to 32 NCQ slots".

So unless these are all addressed, I'd veto removal of the old ATA
driver - sorry!

Best regards
Matthias