On 16/11/2020 09:03, Hannes Reinecke wrote:
On 11/16/20 9:56 AM, John Garry wrote:
On 03/07/2020 14:01, Hannes Reinecke wrote:
Add helper functions to allow LLDDs to allocate and free
internal commands.
Hi Hannes,
Is there any way to ensure that the request allocated is associated
with some determined HW queue here?
The reason for this requirement is that sometimes the LLDD must submit
some internal IO (for which we allocate an "internal command") on a
specific HW queue. An example of this is internal abort IO commands,
which should be submitted on the same queue as the IO which we are
attempting to abort was submitted.
So, for sure, the LLDD does not have to honor the hwq associated with
the request and submit on the desired queue, but then we lose the
blk-mq CPU hotplug protection. And maybe other problems.
One way to achieve this is to run scsi_get_internal_cmd() on a CPU
associated with the desired HW queue, but that's a bit hacky. Not sure
of another way.
Hmm. You are correct for the 'abort' command; that typically needs to be
submitted to a specific hwq.
Let me think about it...
Hannes,
Earlier you mentioned " some drivers not only the command needs a tag,
but the sgls also, thereby completely messing up our mq tags logic.
So to map those we'd need to allocate _several_ tags for one command ..."
Which drivers are these? Can you provide a pointer? Is this the blocker?
Thanks,
John
