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05b40e0577
If the child domain prefers tasks to go siblings, the local group could
end up pulling tasks to itself even if the local group is almost equally
loaded as the source group.
Lets assume a 4 core,smt==2 machine running 5 thread ebizzy workload.
Everytime, local group has capacity and source group has atleast 2 threads,
local group tries to pull the task. This causes the threads to constantly
move between different cores. This is even more profound if the cores have
more threads, like in Power 8, smt 8 mode.
Fix this by only allowing local group to pull a task, if the source group
has more number of tasks than the local group.
Here are the relevant perf stat numbers of a 22 core,smt 8 Power 8 machine.
Without patch:
Performance counter stats for 'ebizzy -t 22 -S 100' (5 runs):
1,440 context-switches # 0.001 K/sec ( +- 1.26% )
366 cpu-migrations # 0.000 K/sec ( +- 5.58% )
3,933 page-faults # 0.002 K/sec ( +- 11.08% )
Performance counter stats for 'ebizzy -t 48 -S 100' (5 runs):
6,287 context-switches # 0.001 K/sec ( +- 3.65% )
3,776 cpu-migrations # 0.001 K/sec ( +- 4.84% )
5,702 page-faults # 0.001 K/sec ( +- 9.36% )
Performance counter stats for 'ebizzy -t 96 -S 100' (5 runs):
8,776 context-switches # 0.001 K/sec ( +- 0.73% )
2,790 cpu-migrations # 0.000 K/sec ( +- 0.98% )
10,540 page-faults # 0.001 K/sec ( +- 3.12% )
With patch:
Performance counter stats for 'ebizzy -t 22 -S 100' (5 runs):
1,133 context-switches # 0.001 K/sec ( +- 4.72% )
123 cpu-migrations # 0.000 K/sec ( +- 3.42% )
3,858 page-faults # 0.002 K/sec ( +- 8.52% )
Performance counter stats for 'ebizzy -t 48 -S 100' (5 runs):
2,169 context-switches # 0.000 K/sec ( +- 6.19% )
189 cpu-migrations # 0.000 K/sec ( +- 12.75% )
5,917 page-faults # 0.001 K/sec ( +- 8.09% )
Performance counter stats for 'ebizzy -t 96 -S 100' (5 runs):
5,333 context-switches # 0.001 K/sec ( +- 5.91% )
506 cpu-migrations # 0.000 K/sec ( +- 3.35% )
10,792 page-faults # 0.001 K/sec ( +- 7.75% )
Which show that in these workloads CPU migrations get reduced significantly.
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/1490205470-10249-1-git-send-email-srikar@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.