On 05/01/2014 11:05 PM, Christoph Hellwig wrote: > On Thu, May 01, 2014 at 08:19:39PM -0600, Jens Axboe wrote: >> I've taken the consequence of this and implemented another tagging >> scheme that blk-mq will use if it deems that percpu_ida isn't going >> to be effective for the device being initialized. But I really hate >> to have both of them in there. Unfortunately I have no devices >> available that have a tag space that will justify using percu_ida, >> so comparisons are a bit hard at the moment. NVMe should change >> that, though, so decision will have to be deferred until that is >> tested. > > At least for SCSI devices _tag space_ is plenty, it's just the we > artifically limit our tag space to the queue depth to avoid having to > track that one separately. In addition we also preallocaste a request > for each tag, so even if we would track the queue depth separately > we would waste a lot of memory.
In practice it comes out to the same, it's not feasible to run a much larger space and track on queue depth. So I don't think that changes the conclusion for SCSI. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/