Re: [PATCH v3 0/5] s390/idle: CPU idle driver

[Christian Loehle]

On 6/19/26 10:29, Alexander Gordeev wrote:
> On Thu, Jun 18, 2026 at 02:00:14PM +0200, Mete Durlu wrote:
> ...
>> This patch series introduces a CPU idle driver for s390 architecture
>> that leverages the existing cpu idle infrastructure and idle governor
>> to optimize idle state selection based on timer events and interrupt
>> patterns.
>>
>> - Implementation Overview
>> -----------------------------------------------------------------------
>>
>> The driver implements two idle states;
>>
>> **Polling Idle (shallow state)**
>> - Busy-loop implementation that prevents SIE-exit during short idle periods
>> - Zero exit latency, optimized for latency-sensitive workloads
>> - Maintains CPU with the guest, improving response times
>>
>> **Enabled Wait (deep state)**
>> - Traditional EW state that signals hypervisor availability
>> - Higher exit latency but more efficient for longer idle periods
>>
>> The idle governor dynamically selects between these states by monitoring
>> next timer interrupts and system interrupt frequency, choosing the most
>> appropriate idle state for each situation.
>>
>> - Performance Benefits
>> -----------------------------------------------------------------------
>>
>> Benchmark results across LPAR, KVM, and z/VM guests demonstrate significant
>> improvements for latency-sensitive and scheduler-intensive workloads:
>>
>> ```
>> Benchmark    | LPAR  | z/VM  | KVM   |
>> -----------------------------------------
>> cyclictest   | +45%  | +50%  | +30%  |
>> hackbench    | +5%   | +12%  | -     |
>> pgbench      | +2%   | +15%  | +2%   |
>> uperf        | +50%* | +-5%  | +-5%  |
>> ```
>>
>> *Single-threaded uperf scenarios show 50-70% improvements on LPAR.
>> Multi-threaded results show slight improvements overall.
>>
>> Additionally, fio and ioping tests show latency distribution shifts toward
>> lower values with reduced minimum and average latencies.
>>
>> - Configuration
>> -----------------------------------------------------------------------
>>
>> Target residency and exit latency values are benchmark estimates. Due to
>> s390's virtualized architecture, these values are non-deterministic.
>> Idle state parameters are tuned per hypervisor type after benchmarks:
>>
>> **LPAR:**
>> - EW: 5us target residency, 5us exit latency
>>
>> **KVM/z/VM:**
>> - EW: 1us target residency, 1us exit latency
>>
>> ---
>> Mete Durlu (5):
>>       s390/tick: Remove CIF_NOHZ_DELAY flag
>>       tick: Remove arch_needs_cpu
>>       s390: Enable TIF_POLLING_NRFLAG
>>       s390/idle: Introduce cpuidle for s390
>>       s390/configs: Enable cpuidle driver on s390
>>
>>  MAINTAINERS                         |   8 +++
>>  arch/s390/Kconfig                   |   5 ++
>>  arch/s390/configs/debug_defconfig   |   2 +
>>  arch/s390/configs/defconfig         |   2 +
>>  arch/s390/include/asm/processor.h   |   4 --
>>  arch/s390/include/asm/thread_info.h |   1 +
>>  arch/s390/kernel/idle.c             |   1 -
>>  arch/s390/kernel/irq.c              |   4 --
>>  arch/s390/kernel/smp.c              |   1 -
>>  drivers/cpuidle/Kconfig             |   5 ++
>>  drivers/cpuidle/Kconfig.s390        |  11 ++++
>>  drivers/cpuidle/Makefile            |   4 ++
>>  drivers/cpuidle/cpuidle-s390.c      | 115 ++++++++++++++++++++++++++++++++++++
>>  include/linux/tick.h                |   3 -
>>  kernel/time/tick-sched.c            |   7 +--
>>  15 files changed, 156 insertions(+), 17 deletions(-)
>> ---
>> base-commit: 2d3090a8aeb596a26935db0955d46c9a5db5c6ce
>> change-id: 20260609-idledriver-217e2b2712a3
>>
>> Best regards,
>> -- 
>> Mete Durlu <meted@xxxxxxxxxxxxx>
> 
> Applied, thanks!

All of it? Rafael should probably at least ack drivers/cpuidle/* things...