From d760fb928c71141689162a4079542f899c8f111a Mon Sep 17 00:00:00 2001 From: Samuel Angebault Date: Sat, 14 Oct 2023 05:24:39 +0200 Subject: [PATCH] Disable CPU C-States other than C1 (#16703) 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 --- files/Aboot/boot0.j2 | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/files/Aboot/boot0.j2 b/files/Aboot/boot0.j2 index c5c6a60aa2..143e869e58 100644 --- a/files/Aboot/boot0.j2 +++ b/files/Aboot/boot0.j2 @@ -615,6 +615,14 @@ write_platform_specific_cmdline() { aboot_machine=arista_7280cr3mk_32p4 flash_size=7382 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 "$platform" "rook" "magpie" "woodpecker" "sprucefish"; then cmdline_add tsc=reliable cmdline_add pcie_ports=native @@ -625,7 +633,6 @@ write_platform_specific_cmdline() { if in_array "$platform" "rook" "sprucefish"; then cmdline_add iommu=on cmdline_add intel_iommu=on - cmdline_add intel_idle.max_cstate=0 read_system_eeprom fi if in_array "$platform" "rook"; then @@ -643,7 +650,6 @@ write_platform_specific_cmdline() { read_system_eeprom fi if in_array "$platform" "lorikeet" "hedgehog"; then - cmdline_add processor.max_cstate=1 cmdline_add reassign_prefmem read_system_eeprom fi