On Tue, Nov 25, 2014 at 03:47:40PM +0100, Hannes Reinecke wrote: > I'd rather have a single map to get request/tags from; otherwise > we'd be arbitrarily starving internal requests even though the > 'main' tag map is empty.
At least in blk-mq the assumption is that a driver needs very few internal tags, and it might need access to them in "emergency" situations like resets or aborts. > My plan was more to mark a certain range of tags as 'reserved', > and add another helper/argument to allow to dip into the reserved > pool, too. We can add this as optional behavior, but I think the existing blk-mq behavior is a good default. > A tentative patch is attached. > Idea is to call blk_queue_init_tags() with the actual tag size and > then blk_resize_tags() to limit the number of tags for the request > queue. > The driver can then use 'blk_allocate_tag' with the appropriate max > depth to get tags from the range [max_depth:real_max_depth]. I'd much prefer the blk-mq approach with two maps. Either way please make sure whatever you come up is compatible with blk-mq. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
