Does anyone actually know why? Pavel didn't seem to, so maybe it
was just disabled on a hunch?
> I tested the patch with a printk() which printed whenever the new call to the
> request function was triggered. It didn't happen once in normal fs use
> with ext2 on a scsi disk. From the code I think its not even possible for
> this to be called at all for a device which has plugging. For a plugged
> device when I/O comes in, there appear to be only two cases:
>
> - Device queue empty. Device gets plugged. New request_fn call not called
> - Device queue not empty. New I/O added to back of queue. New request_fn
> not called (it only gets called when the I/O is added to the front of
> the queue).
Exactly right.
> I think nbd is the only device which doesn't use plugging at the
> moment (from a quick grep of the kernel source),
Probably right -- loop used to disable plugging to disallow merging
and tq_disk deadlocks, but now (-ac) it's a make_request style
driver instead.
-- Jens Axboe- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/