[PATCH 1/2] cfq-iosched: Introduce an ioscheduler tunable "fairness"

[Vivek Goyal <vgoyal@redhat.com>]

o Introduce a tunable "fairness" for CFQ ioscheduler. If this is set, CFQ will
  try to focus more on fairness and disable some of the hooks geared towards
  throughput at the expense of fairness.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 block/cfq-iosched.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 87276eb..658ea7b 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -185,6 +185,7 @@ struct cfq_data {
 	 * Fallback dummy cfqq for extreme OOM conditions
 	 */
 	struct cfq_queue oom_cfqq;
+	unsigned int cfq_fairness;
 };
 
 enum cfqq_state_flags {
@@ -2495,6 +2496,7 @@ static void *cfq_init_queue(struct request_queue *q)
 	cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
 	cfqd->cfq_slice_idle = cfq_slice_idle;
 	cfqd->hw_tag = 1;
+	cfqd->cfq_fairness = 0;
 
 	return cfqd;
 }
@@ -2563,6 +2565,7 @@ SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
 SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
 SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
 SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
+SHOW_FUNCTION(cfq_fairness_show, cfqd->cfq_fairness, 0);
 #undef SHOW_FUNCTION
 
 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)			\
@@ -2594,6 +2597,7 @@ STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
 STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
 STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
 		UINT_MAX, 0);
+STORE_FUNCTION(cfq_fairness_store, &cfqd->cfq_fairness, 0, 1, 0);
 #undef STORE_FUNCTION
 
 #define CFQ_ATTR(name) \
@@ -2609,6 +2613,7 @@ static struct elv_fs_entry cfq_attrs[] = {
 	CFQ_ATTR(slice_async),
 	CFQ_ATTR(slice_async_rq),
 	CFQ_ATTR(slice_idle),
+	CFQ_ATTR(fairness),
 	__ATTR_NULL
 };
 
-- 
1.6.0.6