lkml.org 
[lkml]   [2019]   [Dec]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2] schied/fair: Skip calculating @contrib without load
Date
Because of the:

if (!load)
runnable = running = 0;

clause in ___update_load_sum(), all the actual users of @contrib in
accumulate_sum():

if (load)
sa->load_sum += load * contrib;
if (runnable)
sa->runnable_load_sum += runnable * contrib;
if (running)
sa->util_sum += contrib << SCHED_CAPACITY_SHIFT;

don't happen, and therefore we don't care what @contrib actually is and
calculating it is pointless.

If we count the times when @load equals zero and not as below:

if (load) {
load_is_not_zero_count++;
contrib = __accumulate_pelt_segments(periods,
1024 - sa->period_contrib,delta);
} else
load_is_zero_count++;

As we can see, load_is_zero_count is much bigger than
load_is_zero_count, and the gap is gradually widening:

load_is_zero_count: 6016044 times
load_is_not_zero_count: 244316 times
19:50:43 up 1 min, 1 user, load average: 0.09, 0.06, 0.02

load_is_zero_count: 7956168 times
load_is_not_zero_count: 261472 times
19:51:42 up 2 min, 1 user, load average: 0.03, 0.05, 0.01

load_is_zero_count: 10199896 times
load_is_not_zero_count: 278364 times
19:52:51 up 3 min, 1 user, load average: 0.06, 0.05, 0.01

load_is_zero_count: 14333700 times
load_is_not_zero_count: 318424 times
19:54:53 up 5 min, 1 user, load average: 0.01, 0.03, 0.00

Perhaps we can gain some performance advantage by saving these
unnecessary calculation.

Signed-off-by: Peng Wang <rocking@linux.alibaba.com>
---
kernel/sched/pelt.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index a96db50..4392953 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -129,8 +129,9 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
* Step 2
*/
delta %= 1024;
- contrib = __accumulate_pelt_segments(periods,
- 1024 - sa->period_contrib, delta);
+ if (load)
+ contrib = __accumulate_pelt_segments(periods,
+ 1024 - sa->period_contrib, delta);
}
sa->period_contrib = delta;

--
1.8.3.1
\
 
 \ /
  Last update: 2019-12-13 04:47    [W:0.060 / U:36.716 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site