lkml.org 
[lkml]   [2022]   [Jun]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC v2 03/18] scsi: core: Implement reserved command handling
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@suse.de +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

\
 
 \ /
  Last update: 2022-06-20 13:57    [W:0.077 / U:0.308 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site