The size of struct bfq_iocq_bfqq_data can be reduced by moving a few fields
around.
On a x86_64, with allmodconfig, this shrinks the size from 144 to 128
bytes.
The main benefit is to reduce the size of struct bfq_io_cq from 1360 to
1232.
This structure is stored in a dedicated slab cache. So reducing its size
improves cache usage.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
Compile tested only.
On my system, struct bfq_io_cq are stored in 8 pages slab. Each of these
slabs hold 24 entries.
$ sudo cat /proc/slabinfo | grep bfq_io
bfq_io_cq 378 384 1360 24 8 : tunables 0 0 0 : slabdata 16 16 0
With the new layout, we should store 26 entries.
(8 * 4096 / 1232 = 26.60)
---
block/bfq-iosched.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 687a3a7ba784..0b4704932d72 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -427,9 +427,6 @@ struct bfq_iocq_bfqq_data {
*/
bool saved_IO_bound;
- u64 saved_io_start_time;
- u64 saved_tot_idle_time;
-
/*
* Same purpose as the previous fields for the values of the
* field keeping the queue's belonging to a large burst
@@ -450,6 +447,9 @@ struct bfq_iocq_bfqq_data {
*/
unsigned int saved_weight;
+ u64 saved_io_start_time;
+ u64 saved_tot_idle_time;
+
/*
* Similar to previous fields: save wr information.
*/
@@ -457,13 +457,13 @@ struct bfq_iocq_bfqq_data {
unsigned long saved_last_wr_start_finish;
unsigned long saved_service_from_wr;
unsigned long saved_wr_start_at_switch_to_srt;
- unsigned int saved_wr_cur_max_time;
struct bfq_ttime saved_ttime;
+ unsigned int saved_wr_cur_max_time;
/* Save also injection state */
- u64 saved_last_serv_time_ns;
unsigned int saved_inject_limit;
unsigned long saved_decrease_time_jif;
+ u64 saved_last_serv_time_ns;
/* candidate queue for a stable merge (due to close creation time) */
struct bfq_queue *stable_merge_bfqq;
--
2.50.1
