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Disable CPU C-States other than C1 (#16703)

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Why I did it
Networking devices need to be responsive. Such responsiveness is harmed when the CPU change state.
There is a latency penalty when a CPU is idle (e.g C2) and need to exit this state to come back to C1 state.
To prevent this from happening the CPU should be forced to remain in C1 state.

How I did it
Generalize the cstate forcing to C1 to all Arista products.
This is done by adding processor.max_cstate=1 to the kernel cmdline for all CPUs.
Additionally Intel CPUs also need intel_idle.max_cstate=0 to fallback to the acpi_idle driver.

How to verify it
Check that processor.max_cstate=1 is present on the cmdline for AMD CPUs
Check that both processor.max_cstate=1 and intel_idle.max_cstate=0 are present on the cmdline for Intel CPUs
This commit is contained in:
Samuel Angebault 2023-10-14 05:24:39 +02:00 committed by GitHub
parent f88a5f5d2c
commit d760fb928c
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1 changed files with 8 additions and 2 deletions
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10
files/Aboot/boot0.j2
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@ -615,6 +615,14 @@ write_platform_specific_cmdline() {
aboot_machine=arista_7280cr3mk_32p4 aboot_machine=arista_7280cr3mk_32p4
flash_size=7382 flash_size=7382
fi fi
# disable cpu c-state other than C1
local cpuvendor="$(sed -nr 's/vendor_id[\t ]*: (.*)/\1/p' /proc/cpuinfo | head -n 1)"
cmdline_add processor.max_cstate=1
if [ "$cpuvendor" = "GenuineIntel" ]; then
cmdline_add intel_idle.max_cstate=0
fi
if in_array "$platform" "rook" "magpie" "woodpecker" "sprucefish"; then if in_array "$platform" "rook" "magpie" "woodpecker" "sprucefish"; then
cmdline_add tsc=reliable cmdline_add tsc=reliable
cmdline_add pcie_ports=native cmdline_add pcie_ports=native
@ -625,7 +633,6 @@ write_platform_specific_cmdline() {
if in_array "$platform" "rook" "sprucefish"; then if in_array "$platform" "rook" "sprucefish"; then
cmdline_add iommu=on cmdline_add iommu=on
cmdline_add intel_iommu=on cmdline_add intel_iommu=on
cmdline_add intel_idle.max_cstate=0
read_system_eeprom read_system_eeprom
fi fi
if in_array "$platform" "rook"; then if in_array "$platform" "rook"; then
@ -643,7 +650,6 @@ write_platform_specific_cmdline() {
read_system_eeprom read_system_eeprom
fi fi
if in_array "$platform" "lorikeet" "hedgehog"; then if in_array "$platform" "lorikeet" "hedgehog"; then
cmdline_add processor.max_cstate=1
cmdline_add reassign_prefmem cmdline_add reassign_prefmem
read_system_eeprom read_system_eeprom
fi fi