[PATCH] cfq-iosched: Detect idle process issuing async request

If we are anticipating a sync request from this process and we are
waiting for that and see an async request come in, expire that slice
and move on.

Signed-off-by: Jens Axboe <axboe@suse.de>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index d582433441c502f31d238ee2fc974287e2ec5adb..93ba54605eda98c9c62657e3e461526c34a31a61 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1747,14 +1747,24 @@ cfq_crq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 
        cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);
 
+       cic = crq->io_context;
+
        /*
         * we never wait for an async request and we don't allow preemption
         * of an async request. so just return early
         */
-       if (!cfq_crq_is_sync(crq))
+       if (!cfq_crq_is_sync(crq)) {
+               /*
+                * sync process issued an async request, if it's waiting
+                * then expire it and kick rq handling.
+                */
+               if (cic == cfqd->active_cic &&
+                   del_timer(&cfqd->idle_slice_timer)) {
+                       cfq_slice_expired(cfqd, 0);
+                       cfq_start_queueing(cfqd, cfqq);
+               }
                return;
-
-       cic = crq->io_context;
+       }
 
        cfq_update_io_thinktime(cfqd, cic);
        cfq_update_io_seektime(cfqd, cic, crq);