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Kernel config - Proper processor features for Core M 5Y10
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zhak
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PostPosted: Thu Jul 28, 2016 9:25 pm    Post subject: Kernel config - Proper processor features for Core M 5Y10 Reply with quote

I'm configuring kernel for Intel Core M 5Y10 CPU, and wanted to make sure I get things right.
This CPU has 2 cores/4 threads. Please correct me if I'm wrong, but I need to set the following:
- Maximum number of CPUs (NR_CPUS) = 3 -- since it has only 2 cores
- SMT (Hyperthreading) scheduler support (SCHED_SMT) = y -- since it supports Intel Hyper-Threading Technology
- Multi-core scheduler support (SCHED_MC) = y -- since it's multi-core
- NUMA support - disabled

Thanks in advance
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trubicoid
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PostPosted: Mon Aug 29, 2016 1:41 pm    Post subject: Reply with quote

NR_CPUS should be 4, but I would not set it, instead set MAXSMP to Y

Quote:
CONFIG_MAXSMP:
Enable maximum number of CPUS and NUMA Nodes for this architecture.


otherwise you're correct
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Hu
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PostPosted: Tue Aug 30, 2016 1:46 am    Post subject: Reply with quote

trubicoid: No, MAXSMP should not be set to Y. From Kconfig NR_CPUS defaults:
Kconfig:
   default "1" if !SMP
   default "8192" if MAXSMP
   default "32" if SMP && X86_BIGSMP
   default "8" if SMP && X86_32
   default "64" if SMP

NR_CPUS should be the number of CPUs you want the kernel to be able to manage. On a single-socket, multi-core system, it should be the number of cores. If the system is hyperthread capable in hardware, and hyperthreading is enabled in the BIOS, NR_CPUS should be adjusted to treat each hyperthread as a separate CPU. Historically, hyperthread capable CPUs had two hyperthread processors per-core, so a quad-core with hyperthreading would choose NR_CPUS=8. Ark says you have two cores, and with hyperthreading that would give you four effective cores, so you should set NR_CPUS=4 if you enable hyperthreading in the BIOS or NR_CPUS=2 if you disable hyperthreading in the BIOS. Why did you suggest NR_CPUS=3?
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trubicoid
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PostPosted: Sun Sep 11, 2016 8:31 pm    Post subject: Reply with quote

interesting, I thought MAXSMP detects the number of CPU during the boot
8k CPUs is too much :D
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