On Wed, 2015-06-03 at 14:57 +0200, Christoph Hellwig wrote: > This makes lockdep very unhappy, rightly so. If you execute > one end_io function inside another you basіcally nest every possible > lock taken in the I/O completion path. Also adding more work > to the hardirq path generally isn't a smart idea. Can you explain > what issues you were seeing and how much this helps? Note that > the workqueue usage in the target core so far is fairly basic, so > there should some low hanging fruit. So I've been using tcm_loop + RAMDISK backends for prototyping, but this patch is intended for vhost-scsi so it can avoid the unnecessary queue_work() context switch within target_complete_cmd() for all backend driver types. This is because vhost_work_queue() is just updating vhost_dev->work_list and immediately wake_up_process() into a different vhost_worker() process context. For heavy small block workloads into fast IBLOCK backends, avoiding this extra context switch should be a nice efficiency win. Also, AFAIK RDMA fabrics are allowed to do ib_post_send() response callbacks directly from IRQ context as well. Perhaps tcm_loop LLD code should just be limited to RAMDISK here..? -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
