From 92ff3dfd8465fcf2e1e6ce95125c76f88e476cac Mon Sep 17 00:00:00 2001 From: John Audia Date: Fri, 9 Jan 2026 08:16:09 -0500 Subject: [PATCH] x86: switch from CONFIG_HZ_PERIODIC to CONFIG_NO_HZ_IDLE MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Running with CONFIG_HZ_PERIODIC=y keeps the scheduler tick running continuously, which produces higher jitter and lower power efficiency. In contrast, CONFIG_NO_HZ_IDLE=y (the upstream default) stops the tick only when the CPU is idle, giving lower idle power and normal runtime jitter. An Intel N150-based router/firewall was tested using two kernel builds: one with CONFIG_HZ_PERIODIC=y, and one with CONFIG_NO_HZ_IDLE=y. Power consumption was measured while the system was essentially idle (no meaningful traffic). The CONFIG_NO_HZ_IDLE=y build consistently used less power. Details: The two power-measurement methods were: 1. PkgWatt from turbostat (software) 2. Wall-power measurement using a Kill-A-Watt (hardware) The test began by zeroing the Kill-A-Watt and simultaneously running: turbostat --quiet --Summary --interval 10 --show Busy%,PkgWatt The test duration was defined by the time required for the Kill-A-Watt to accumulate 0.005 kWh, after which the average wattage was calculated. Results: +----------------------+-----------------+----------------+-----------+ | Metric | HZ_PERIODIC | NO_HZ_IDLE | Delta % | +----------------------+-----------------+----------------+-----------+ | PkgWatt | 3.59 ± 0.38 | 3.38 ± 0.34 | -5.9 % | +----------------------+-----------------+----------------+-----------+ | Avg wattage at wall | 12.47 | 12.00 | -3.77 % | +----------------------+-----------------+----------------+-----------+ The mean PkgWatt difference is 210 mW (5.9%) in favor of CONFIG_NO_HZ_IDLE=y, with a t-statistic of ~3.17 and p ≈ 0.002. Wall-power measurements show a 470 mW (3.77%) reduction under CONFIG_NO_HZ_IDLE=y. Signed-off-by: John Audia Link: https://github.com/openwrt/openwrt/pull/21470 Signed-off-by: Robert Marko --- target/linux/x86/config-6.12 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/target/linux/x86/config-6.12 b/target/linux/x86/config-6.12 index 5fb0d2885b5..581e5a54a5e 100644 --- a/target/linux/x86/config-6.12 +++ b/target/linux/x86/config-6.12 @@ -184,7 +184,6 @@ CONFIG_HW_RANDOM=y CONFIG_HW_RANDOM_GEODE=y CONFIG_HW_RANDOM_VIA=y # CONFIG_HYPERVISOR_GUEST is not set -CONFIG_HZ_PERIODIC=y CONFIG_I2C=y CONFIG_I2C_ALGOBIT=y CONFIG_I2C_BOARDINFO=y @@ -325,6 +324,7 @@ CONFIG_NLS=y # CONFIG_NMI_CHECK_CPU is not set # CONFIG_NOHIGHMEM is not set CONFIG_NO_HZ=y +CONFIG_NO_HZ_IDLE=y CONFIG_NR_CPUS=1 CONFIG_NR_CPUS_DEFAULT=1 CONFIG_NR_CPUS_RANGE_BEGIN=1 -- 2.47.3