Re: [RFC] sched: The removal of idle_balance()
From: Mike Galbraith
Date: Sun Feb 17 2013 - 01:26:25 EST
On Sat, 2013-02-16 at 11:12 -0500, Steven Rostedt wrote:
> On Fri, 2013-02-15 at 08:26 +0100, Mike Galbraith wrote:
> > On Fri, 2013-02-15 at 01:13 -0500, Steven Rostedt wrote:
> >
> > > Think about it some more, just because we go idle isn't enough reason to
> > > pull a runable task over. CPUs go idle all the time, and tasks are woken
> > > up all the time. There's no reason that we can't just wait for the sched
> > > tick to decide its time to do a bit of balancing. Sure, it would be nice
> > > if the idle CPU did the work. But I think that frame of mind was an
> > > incorrect notion from back in the early 2000s and does not apply to
> > > today's hardware, or perhaps it doesn't apply to the (relatively) new
> > > CFS scheduler. If you want aggressive scheduling, make the task rt, and
> > > it will do aggressive scheduling.
> >
> > (the throttle is supposed to keep idle_balance() from doing severe
> > damage, that may want a peek/tweak)
> >
> > Hackbench spreads itself with FORK/EXEC balancing, how does say a kbuild
> > do with no idle_balance()?
> >
>
> Interesting, I added this patch and it brought down my hackbench to the
> same level as removing idle_balance().
The typo did it's job well :)
Hrm, turning idle balancing off here does not help hackbench at all.
3.8.0-master
Q6600 +SD_BALANCE_NEWIDLE
Performance counter stats for 'hackbench -l 500' (100 runs):
5221.559519 task-clock # 4.001 CPUs utilized ( +- 0.26% ) [100.00%]
129863 context-switches # 0.025 M/sec ( +- 3.65% ) [100.00%]
7576 cpu-migrations # 0.001 M/sec ( +- 4.60% ) [100.00%]
31095 page-faults # 0.006 M/sec ( +- 0.39% )
12258227539 cycles # 2.348 GHz ( +- 0.27% ) [49.91%]
<not supported> stalled-cycles-frontend
<not supported> stalled-cycles-backend
5395089628 instructions # 0.44 insns per cycle ( +- 0.28% ) [74.99%]
1012563262 branches # 193.920 M/sec ( +- 0.28% ) [75.08%]
43217098 branch-misses # 4.27% of all branches ( +- 0.23% ) [75.01%]
1.305024749 seconds time elapsed ( +- 0.26% )
Q6600 -SD_BALANCE_NEWIDLE
Performance counter stats for 'hackbench -l 500' (100 runs):
5356.549500 task-clock # 4.001 CPUs utilized ( +- 0.37% ) [100.00%]
153093 context-switches # 0.029 M/sec ( +- 3.20% ) [100.00%]
6887 cpu-migrations # 0.001 M/sec ( +- 4.65% ) [100.00%]
31248 page-faults # 0.006 M/sec ( +- 0.48% )
12141992004 cycles # 2.267 GHz ( +- 0.30% ) [49.90%]
<not supported> stalled-cycles-frontend
<not supported> stalled-cycles-backend
5426436261 instructions # 0.45 insns per cycle ( +- 0.22% ) [75.00%]
1016967893 branches # 189.855 M/sec ( +- 0.22% ) [75.09%]
43207200 branch-misses # 4.25% of all branches ( +- 0.13% ) [75.01%]
1.338768889 seconds time elapsed ( +- 0.37% )
E5620+HT +SD_BALANCE_NEWIDLE
Performance counter stats for 'hackbench -l 500' (100 runs):
3884.162557 task-clock # 7.997 CPUs utilized ( +- 0.14% ) [100.00%]
97366 context-switches # 0.025 M/sec ( +- 1.68% ) [100.00%]
12383 CPU-migrations # 0.003 M/sec ( +- 3.29% ) [100.00%]
30749 page-faults # 0.008 M/sec ( +- 0.13% )
9377671582 cycles # 2.414 GHz ( +- 0.11% ) [83.04%]
6973792586 stalled-cycles-frontend # 74.37% frontend cycles idle ( +- 0.15% ) [83.27%]
2529338603 stalled-cycles-backend # 26.97% backend cycles idle ( +- 0.32% ) [66.93%]
5214109586 instructions # 0.56 insns per cycle
# 1.34 stalled cycles per insn ( +- 0.07% ) [83.50%]
984681811 branches # 253.512 M/sec ( +- 0.07% ) [83.56%]
7050196 branch-misses # 0.72% of all branches ( +- 0.49% ) [83.24%]
0.485726223 seconds time elapsed ( +- 0.14% )
E5620+HT -SD_BALANCE_NEWIDLE
Performance counter stats for 'hackbench -l 500' (100 runs):
4124.204725 task-clock # 7.996 CPUs utilized ( +- 0.20% ) [100.00%]
151292 context-switches # 0.037 M/sec ( +- 1.49% ) [100.00%]
12504 CPU-migrations # 0.003 M/sec ( +- 2.84% ) [100.00%]
30685 page-faults # 0.007 M/sec ( +- 0.07% )
9566938118 cycles # 2.320 GHz ( +- 0.16% ) [83.09%]
7483411444 stalled-cycles-frontend # 78.22% frontend cycles idle ( +- 0.22% ) [83.21%]
2848475061 stalled-cycles-backend # 29.77% backend cycles idle ( +- 0.38% ) [66.82%]
5360541017 instructions # 0.56 insns per cycle
# 1.40 stalled cycles per insn ( +- 0.11% ) [83.48%]
1011027557 branches # 245.145 M/sec ( +- 0.11% ) [83.59%]
7964016 branch-misses # 0.79% of all branches ( +- 0.55% ) [83.32%]
0.515779138 seconds time elapsed ( +- 0.20% )
-Mike
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