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authorShaohua Li <shaohua.li@intel.com>2010-03-01 09:20:54 +0100
committerJens Axboe <jens.axboe@oracle.com>2010-03-01 09:20:54 +0100
commitabc3c744d0d7f4ad710a948ae73852ffea5fbc3b (patch)
treef3aebe4f1ee8138db560b049f84d30a4b7348e8a /block
parentblktrace: perform cleanup after setup error (diff)
downloadlinux-dev-abc3c744d0d7f4ad710a948ae73852ffea5fbc3b.tar.xz
linux-dev-abc3c744d0d7f4ad710a948ae73852ffea5fbc3b.zip
cfq-iosched: quantum check tweak
Currently a queue can only dispatch up to 4 requests if there are other queues. This isn't optimal, device can handle more requests, for example, AHCI can handle 31 requests. I can understand the limit is for fairness, but we could do a tweak: if the queue still has a lot of slice left, sounds we could ignore the limit. Test shows this boost my workload (two thread randread of a SSD) from 78m/s to 100m/s. Thanks for suggestions from Corrado and Vivek for the patch. Signed-off-by: Shaohua Li <shaohua.li@intel.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block')
-rw-r--r--block/cfq-iosched.c30
1 files changed, 26 insertions, 4 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f27e535ce262..0db07d7771b5 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -19,7 +19,7 @@
* tunables
*/
/* max queue in one round of service */
-static const int cfq_quantum = 4;
+static const int cfq_quantum = 8;
static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
/* maximum backwards seek, in KiB */
static const int cfq_back_max = 16 * 1024;
@@ -2197,6 +2197,19 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd)
return dispatched;
}
+static inline bool cfq_slice_used_soon(struct cfq_data *cfqd,
+ struct cfq_queue *cfqq)
+{
+ /* the queue hasn't finished any request, can't estimate */
+ if (cfq_cfqq_slice_new(cfqq))
+ return 1;
+ if (time_after(jiffies + cfqd->cfq_slice_idle * cfqq->dispatched,
+ cfqq->slice_end))
+ return 1;
+
+ return 0;
+}
+
static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
unsigned int max_dispatch;
@@ -2213,7 +2226,7 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
return false;
- max_dispatch = cfqd->cfq_quantum;
+ max_dispatch = max_t(unsigned int, cfqd->cfq_quantum / 2, 1);
if (cfq_class_idle(cfqq))
max_dispatch = 1;
@@ -2230,13 +2243,22 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
/*
* We have other queues, don't allow more IO from this one
*/
- if (cfqd->busy_queues > 1)
+ if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq))
return false;
/*
* Sole queue user, no limit
*/
- max_dispatch = -1;
+ if (cfqd->busy_queues == 1)
+ max_dispatch = -1;
+ else
+ /*
+ * Normally we start throttling cfqq when cfq_quantum/2
+ * requests have been dispatched. But we can drive
+ * deeper queue depths at the beginning of slice
+ * subjected to upper limit of cfq_quantum.
+ * */
+ max_dispatch = cfqd->cfq_quantum;
}
/*