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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 <therealgraysky@proton.me> Link: https://github.com/openwrt/openwrt/pull/21470 Signed-off-by: Robert Marko <robimarko@gmail.com> |
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| base-files | ||
| generic | ||
| geode | ||
| image | ||
| legacy | ||
| patches-6.12 | ||
| base-files.mk | ||
| config-6.12 | ||
| Makefile | ||
| modules.mk | ||