@@ -268,6 +268,15 @@ static struct kmem_cache *bfq_pool;
*/
#define BFQ_RATE_SHIFT 16
+/*
+ * 1) bfq keep dispatching requests with same size for at least one second.
+ * 2) bfq dispatch at lease 1024 requests
+ *
+ * We think bfq are dispatching request with same size if the above two
+ * conditions hold true.
+ */
+#define VARIED_REQUEST_SIZE(bfqd) ((bfqd)->dispatch_count < 1024 ||\
+ time_before(jiffies, (bfqd)->dispatch_time + HZ))
/*
* When configured for computing the duration of the weight-raising
* for interactive queues automatically (see the comments at the
@@ -724,7 +733,8 @@ static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
bool multiple_classes_busy;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
- if (bfqd->num_groups_with_pending_reqs > 1)
+ if (bfqd->num_groups_with_pending_reqs > 1 &&
+ VARIED_REQUEST_SIZE(bfqd))
return true;
#endif
There is a special case when bfq do not need to idle when more than one groups is active: 1) all active queues have the same weight, 2) all active queues have the same request size. 3) all active queues belong to the same I/O-priority class, Each time a request is dispatched, bfq can switch in service queue safely, since the throughput of each active queue is guaranteed to be equivalent. Test procedure: run "fio -numjobs=1 -ioengine=psync -bs=4k -direct=1 -rw=randread..." in different cgroup(not root). Test result: total bandwidth(Mib/s) | total jobs | before this patch | after this patch | | ---------- | ----------------- | --------------------- | | 1 | 33.8 | 33.8 | | 2 | 33.8 | 65.4 (32.7 each job) | | 4 | 33.8 | 106.8 (26.7 each job) | | 8 | 33.8 | 126.4 (15.8 each job) | Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- block/bfq-iosched.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)