On 6/20/22 13:24, Damien Le Moal wrote:
On 6/20/22 18:05, Christoph Hellwig wrote:
On Mon, Jun 20, 2022 at 06:02:30PM +0900, Damien Le Moal wrote:
So reserving a tag/req to be able to do NCQ at the cost of max qd being 31
works for that. We could keep max qd at 32 by creating one more "fake" tag
and having a request for it, that is, having the fake tag visible to the
block layer as a reserved tag, as John's series is doing, but for the
reserved tags, we actually need to use an effective tag (qc->hw_tag) when
issuing the commands. And for that, we can reuse the tag of one of the
failed commands.
Take a look at the magic flush request in blk-flush.c, which is
preallocated but borrows a tag from the request that wants a pre- or
post-flush. The logic is rather ugly, but maybe it might actually
become cleaner by generalizing it a bit.
Thanks. Will check.
I am also looking at scsi_unjam_host() and scsi_eh_get_sense(). These
reuse a scsi command to do eh operations. So I could use that too, modulo
making it work outside of eh context to keep the command flow intact.
Tsk. I was hoping to be able to remove it (especially
scsi_eh_get_sense()), but looks as if we actually do need it.
But it might be not a bad idea to have scsi_eh_get_sense() to run
independent on the SCSI EH stuff; returning with a sense code is not
necessary an error, so there are reasons for not always invoking SCSI EH.
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
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