4e35b475a1
We used to always determine the number of CPU dies by counting unique values in `/sys/devices/system/cpu/cpu*/topology/die_id` files. This method works on x64 systems but is ineffective on ARM64. The `topology_die_id` function is defined for x64 architectures in `arch/x86/include/asm/topology.h` but is not implemented for ARM64 in `arch/arm64/include/asm/topology.h`. In Linux kernel 5.15 (used in Ubuntu 22.04), the `die_id` attribute is exposed with a value of -1 if `topology_die_id` is not defined for the architecture. Therefore, the `die_id` file for ARM64 consistently has the value -1, causing our method of counting unique values to always return 1 on Ubuntu 22.04, regardless of the actual number of dies. This can cause issues if number of sockets is more than 1, since our code assumes `total_dies` is a multiple of `total_sockets`. Starting with Linux kernel 5.17, a change was introduced [1] to expose the `die_id` file only if `topology_die_id` is defined for the architecture. Consequently, in Linux kernel 6.8 (used in Ubuntu 24.04), this file is absent for ARM64 systems. As a result, our method of counting unique values now produces 0 on Ubuntu 24.04. Given the lack of a straightforward way to determine the number of dies on ARM64 systems, this patch sets `total_dies` equal to `total_sockets`, assuming one die per socket. [1] https://github.com/torvalds/linux/commit/2c4dcd7
41 lines
1.2 KiB
Ruby
41 lines
1.2 KiB
Ruby
# frozen_string_literal: true
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class Prog::LearnCpu < Prog::Base
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subject_is :sshable
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CpuTopology = Struct.new(:total_cpus, :total_cores, :total_dies, :total_sockets, keyword_init: true)
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def get_arch
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arch = sshable.cmd("common/bin/arch").strip
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fail "BUG: unexpected CPU architecture" unless ["arm64", "x64"].include?(arch)
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arch
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end
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def get_topology
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s = sshable.cmd("/usr/bin/lscpu -Jye")
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parsed = JSON.parse(s).fetch("cpus").map { |cpu|
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[cpu.fetch("socket"), cpu.fetch("core")]
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}
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cpus = parsed.count
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sockets = parsed.map { |socket, _| socket }.uniq.count
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cores = parsed.uniq.count
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CpuTopology.new(total_cpus: cpus, total_cores: cores, total_dies: 0,
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total_sockets: sockets)
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end
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def count_dies(arch:, total_sockets:)
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# Linux kernel doesn't provide die_id information for arm64.
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return total_sockets if arch == "arm64"
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die_ids = sshable.cmd("cat /sys/devices/system/cpu/cpu*/topology/die_id").split("\n")
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die_ids.uniq.count
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end
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label def start
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arch = get_arch
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topo = get_topology
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topo.total_dies = count_dies(total_sockets: topo.total_sockets, arch: arch)
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pop(arch: arch, **topo.to_h)
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end
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end
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