How do I restrict the number of CPUs used by Linux on a multicore CPS?

[ChrisImgtecModerator]

You can restrict the number of CPUs used by Linux with the
isolcpus boot option:

Name
isolcpus – isolate CPUs from the kernel scheduler.

Synopsis
isolcpus= cpu_number [, cpu_number ,…]

Description
Remove the specified CPUs, as defined by the cpu_number
values, from the general kernel SMP balancing and scheduler
algroithms. The only way to move a process onto or off an
“isolated” CPU is via the CPU affinity syscalls. cpu_number
begins at 0, so the maximum value is 1 less than the number
of CPUs on the system.

This option is the preferred way to isolate CPUs. The
alternative–manually setting the CPU mask of all tasks in
the system–can cause problems and suboptimal load balancer
performance.

So for a Mulit threaded 3-core (6-CPU) CPS, if you want to restrict
the number of cores to 1, you would add the following to
your boot command:

isolcpus=2,3,4,5

And if you want to restrict the number of cores to 2:

isolcpus=4,5

To restrict the number of VPEs per core to 1:

isolcpus=1,3,5

Here is the output of ‘mpstat -P ALL’ after I boot my 3 core
1004K Malta with isolcpus=1,3,5:

-sh-4.1# mpstat -P ALL
Linux 2.6.32-ts-mipsisa32r2cmp (malta_le_hf) 05/11/11 _mips_ (6 CPU)

10:29:51 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle
10:29:51 all 3.19 0.00 3.05 0.12 0.03 0.01 0.00 0.00 93.60
10:29:51 0 7.62 0.00 12.57 0.25 0.17 0.02 0.00 0.00 79.37
10:29:51 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:29:51 2 6.80 0.00 3.43 0.27 0.00 0.01 0.00 0.00 89.49
10:29:51 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:29:51 4 4.74 0.00 2.28 0.20 0.00 0.01 0.00 0.00 92.77
10:29:51 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
-sh-4.1#

As you can see, CPUs 1, 3, and 5 are 100% idle because they
are isolated from the kernel scheduler.

[ChrisImgtecModerator]

Imagination MIPS Support

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