On 02/23/10 01:21, Jens Axboe wrote:
On Mon, Feb 22 2010, Robert Hancock wrote:
On Mon, Feb 22, 2010 at 3:49 PM, Mark Lord<kernel@xxxxxxxxxxxx> wrote:
On 02/22/10 14:05, Jens Axboe wrote:
--- a/block/blk-core.c
+++ b/block/blk-core.c
...
@@ -1857,8 +1857,15 @@ void blk_dequeue_request(struct request *rq)
* and to it is freed is accounted as io that is in progress at
* the driver side.
*/
- if (blk_account_rq(rq))
+ if (blk_account_rq(rq)) {
q->in_flight[rq_is_sync(rq)]++;
+ /*
+ * Mark this device as supporting hardware queuing, if
+ * we have more IOs in flight than 4.
+ */
+ if (!blk_queue_queuing(q)&& queue_in_flight(q)> 4)
+ set_bit(QUEUE_FLAG_CQ,&q->queue_flags);
+ }
}
...
Mmm.. So is this code actually trying to rely upon the software being quick
enough to queue five or more commands before the drive completes one of
them?
Yes, it'll trigger easily. If it's the boot drive, it'll be on before
booting has completed.
...
Mmm.. but that all assumes (1) a fast CPU and (2) a slow mechanical drive.
Neither of which are true in many modern systems.
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