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Date: Wed, 13 Oct 2010 12:09:34 -0700
From: Nikhil Rao <ncrao@...gle.com>
To: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
Mike Galbraith <efault@....de>,
Suresh Siddha <suresh.b.siddha@...el.com>,
Venkatesh Pallipadi <venki@...gle.com>
Cc: linux-kernel@...r.kernel.org, Nikhil Rao <ncrao@...gle.com>
Subject: [PATCH 0/4][RFC v2] Improve load balancing when tasks have large weight differential
Hi all,
Please find attached a series of patches that improve load balancing when
there is a large weight differential between tasks (such as when nicing a task
or when using SCHED_IDLE). These patches are based off feedback given by Peter
Zijlstra and Mike Galbraith in earlier posts.
Previous versions:
-v0: http://thread.gmane.org/gmane.linux.kernel/1015966
Large weight differential leads to inefficient load balancing
-v1: http://thread.gmane.org/gmane.linux.kernel/1041721
Improve load balancing when tasks have large weight differential
These patches can be applied to v2.6.36-rc7 or -tip without conflicts. Below
are some tests that highlight the improvements with this patchset.
1. 16 SCHED_IDLE soakers, 1 SCHED_NORMAL task on 16 cpu machine.
Tested on a quad-cpu, quad-socket. Steps to reproduce:
- spawn 16 SCHED_IDLE tasks
- spawn one nice 0 task
- system utilization immediately drops to 80% on v2.6.36-rc7
v2.6.36-rc7
10:38:46 AM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
10:38:47 AM all 80.69 0.00 0.50 0.00 0.00 0.00 0.00 18.82 14008.00
10:38:48 AM all 85.09 0.06 0.50 0.00 0.00 0.00 0.00 14.35 14690.00
10:38:49 AM all 86.83 0.06 0.44 0.00 0.00 0.00 0.00 12.67 14314.85
10:38:50 AM all 79.89 0.00 0.37 0.00 0.00 0.00 0.00 19.74 14035.35
10:38:51 AM all 87.94 0.06 0.44 0.00 0.00 0.00 0.00 11.56 14991.00
10:38:52 AM all 83.27 0.06 0.37 0.00 0.00 0.00 0.00 16.29 14319.00
10:38:53 AM all 94.37 0.13 0.50 0.00 0.00 0.00 0.00 5.00 15930.00
10:38:54 AM all 87.06 0.06 0.62 0.00 0.00 0.06 0.00 12.19 14946.00
10:38:55 AM all 88.68 0.06 0.38 0.00 0.00 0.00 0.00 10.88 14767.00
10:38:56 AM all 80.16 0.00 1.06 0.00 0.00 0.00 0.00 18.78 13892.08
Average: all 85.38 0.05 0.52 0.00 0.00 0.01 0.00 14.05 14588.91
v2.6.36-rc7 + patchset:
10:40:31 AM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
10:40:32 AM all 99.25 0.00 0.75 0.00 0.00 0.00 0.00 0.00 16998.00
10:40:33 AM all 99.75 0.00 0.19 0.00 0.00 0.06 0.00 0.00 16337.00
10:40:34 AM all 98.75 0.00 1.25 0.00 0.00 0.00 0.00 0.00 17127.27
10:40:35 AM all 99.06 0.00 0.94 0.00 0.00 0.00 0.00 0.00 16741.58
10:40:36 AM all 99.50 0.06 0.44 0.00 0.00 0.00 0.00 0.00 16477.00
10:40:37 AM all 99.50 0.00 0.50 0.00 0.00 0.00 0.00 0.00 16868.69
10:40:38 AM all 99.13 0.00 0.81 0.00 0.00 0.06 0.00 0.00 16761.39
10:40:39 AM all 99.19 0.00 0.81 0.00 0.00 0.00 0.00 0.00 17501.00
10:40:40 AM all 99.94 0.00 0.06 0.00 0.00 0.00 0.00 0.00 18209.00
10:40:41 AM all 99.19 0.00 0.81 0.00 0.00 0.00 0.00 0.00 16862.00
Average: all 99.32 0.01 0.66 0.00 0.00 0.01 0.00 0.00 16987.80
2. Sub-optimal utilizataion in presence of niced task.
Tested on a dual-socket/quad-core w/ two cores on each socket disabled.
Steps to reproduce:
- spawn 4 nice 0 soakers and one nice -15 soaker
- force all tasks onto one cpu by setting affinities
- reset affinity masks
v2.6.36-rc7:
Cpu(s): 34.3% us, 0.2% sy, 0.0% ni, 65.1% id, 0.4% wa, 0.0% hi, 0.0% si
Mem: 16463308k total, 996368k used, 15466940k free, 12304k buffers
Swap: 0k total, 0k used, 0k free, 756244k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
7651 root 5 -15 5876 84 0 R 98 0.0 37:35.97 soaker
7652 root 20 0 5876 84 0 R 49 0.0 19:49.02 soaker
7654 root 20 0 5876 84 0 R 49 0.0 20:48.93 soaker
7655 root 20 0 5876 84 0 R 49 0.0 19:25.74 soaker
7653 root 20 0 5876 84 0 R 47 0.0 20:02.16 soaker
v2.6.36-rc7 + patchset:
Cpu(s): 49.7% us, 0.2% sy, 0.0% ni, 50.2% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 16463308k total, 1011248k used, 15452060k free, 10076k buffers
Swap: 0k total, 0k used, 0k free, 766388k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
7645 root 5 -15 5876 88 0 R 100 0.0 43:38.76 soaker
7646 root 20 0 5876 88 0 R 99 0.0 33:15.25 soaker
7648 root 20 0 5876 88 0 R 75 0.0 36:57.02 soaker
7647 root 20 0 5876 88 0 R 67 0.0 29:12.97 soaker
7649 root 20 0 5876 88 0 R 54 0.0 29:28.35 soaker
Comments, feedback welcome.
-Thanks,
Nikhil
Nikhil Rao (4):
sched: do not consider SCHED_IDLE tasks to be cache hot
sched: set group_imb only a task can be pulled from the busiest cpu
sched: drop group_capacity to 1 only if local group has extra
capacity
sched: force balancing on newidle balance if local group has capacity
kernel/sched.c | 3 +++
kernel/sched_fair.c | 48 ++++++++++++++++++++++++++++++++++++++++--------
2 files changed, 43 insertions(+), 8 deletions(-)
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