On 13/06/2022 10:43, Damien Le Moal wrote:
Currently, that is not possible to do cleanly as there are no guarantees
we can get a free tag (there is a race between block layer tag allocation
and libata internal tag counting). So a reserved tag for that would be
nice. We would end up with 31 IO tags at most + 1 reserved tag for NCQ
commands + ATA_TAG_INTERNAL for non-NCQ. That last one would be rendered
rather useless. But that also means that we kind-of go back to the days
when Linux showed ATA drives max QD of 31...
So must the ATA_TAG_INTERNAL qc always be available for non-NCQ action
like EH, and that is why you cannot reuse for this internal NCQ
(queuable) command?
Currently, ATA_TAG_INTERNAL is always used for non-NCQ commands. Seeing a
qc with that tag means it is*not* NCQ.
I am trying to see if I can reuse the tag from one of the commands that
completed with that weird good status/sense data available. The problem
though is that this all needs to be done*before* calling
qc->complete_fn() which will free the tag. So we endup with 2 qcs that
have the same tag, the second one (for the read log command) temporarily
using the tag but still going through the same completion path without the
original command fully completed yet. It is a real mess.
Reusing tags seems really messy, but then reserving an NCQ command seems
wasteful.
Thanks,
John
