| From | Thomas Gleixner <> | Subject | [patch 00/10] x86/cpu: Consolidate APERF/MPERF code | Date | Fri, 15 Apr 2022 21:19:48 +0200 (CEST) |
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APERF/MPERF is utilized in two ways:
1) Ad hoc readout of CPU frequency which requires IPIs
2) Frequency scale calculation for frequency invariant scheduling which reads APERF/MPERF on every tick.
These are completely independent code parts. Eric observed long latencies when reading /proc/cpuinfo which reads out CPU frequency via #1 and proposed to replace the per CPU single IPI with a broadcast IPI.
While this makes the latency smaller, it is not necessary at all because #2 samples APERF/MPERF periodically, except on idle or isolated NOHZ full CPUs which are excluded from IPI already.
It could be argued that not all APERF/MPERF capable systems have the required BIOS information to enable frequency invariance support, but in practice most of them do. So the APERF/MPERF sampling can be made unconditional and just the frequency scale calculation for the scheduler excluded.
The following series consolidates that.
Thanks,
tglx --- arch/x86/include/asm/cpu.h | 2 arch/x86/include/asm/topology.h | 17 - arch/x86/kernel/acpi/cppc.c | 28 -- arch/x86/kernel/cpu/aperfmperf.c | 474 +++++++++++++++++++++++++++++++-------- arch/x86/kernel/cpu/proc.c | 2 arch/x86/kernel/smpboot.c | 358 ----------------------------- fs/proc/cpuinfo.c | 6 include/linux/cpufreq.h | 1 8 files changed, 405 insertions(+), 483 deletions(-)
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