On 3/11/20 7:22 AM, Christoph Hellwig wrote: > On Tue, Mar 10, 2020 at 09:08:56PM +0000, John Garry wrote: >> On 10/03/2020 18:32, Christoph Hellwig wrote: >>> On Wed, Mar 11, 2020 at 12:25:28AM +0800, John Garry wrote: >>>> From: Hannes Reinecke <hare@xxxxxxxx> >>>> >>>> Allocate a separate 'reserved_cmd_q' for sending reserved commands. >>> >>> Why? Reserved command specifically are not in any way tied to queues. >>> . >>> >> >> So the v1 series used a combination of the sdev queue and the per-host >> reserved_cmd_q. Back then you questioned using the sdev queue for virtio >> scsi, and the unconfirmed conclusion was to use a common per-host q. This is >> the best link I can find now: >> >> https://www.mail-archive.com/linux-scsi@xxxxxxxxxxxxxxx/msg83177.html > > That was just a question on why virtio uses the per-device tags, which > didn't look like it made any sense. What I'm worried about here is > mixing up the concept of reserved tags in the tagset, and queues to use > them. Note that we already have the scsi_get_host_dev to allocate > a scsi_device and thus a request_queue for the host itself. That seems > like the better interface to use a tag for a host wide command vs > introducing a parallel path. > Ah. Right. Will be looking into that, and convert the patchset over to it. And the problem of the separate queue is the fact that I'll need a queue to reserve tags from; trying to allocate a tag directly from the bitmap turns out to be major surgery in the blocklayer with no immediate gain. And I can't use per-device queues as for some drivers the reserved commands are used to query the HBA itself to figure out how many devices are present. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
