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Wysocki" , Daniel Lezcano , Christian Loehle , Christian Borntraeger , Ilya Leoshkevich , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [PATCH v3 0/5] s390/idle: CPU idle driver Message-ID: References: <20260618-idledriver-v3-0-684061eecbcb@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260618-idledriver-v3-0-684061eecbcb@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Info: AW1haW4tMjYwNjE5MDA4NiBTYWx0ZWRfX4ezXzYeVpJLz b/MZQ7TjblzDPAvAyZ1N8ybxBJQAv0P3nZMQNtqNx0j6OpgjJMp/YlQaQBGwHX2DXew7EK53fKF tExlV4vhN79hRNqmDhywPh8/EnqRrxs= X-Proofpoint-GUID: abg4Ryfq43opm4tU6yzG9rDjiSF8_WmZ X-Authority-Analysis: v=2.4 cv=bMgm5v+Z c=1 sm=1 tr=0 ts=6a350bf8 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=kj9zAlcOel0A:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=qNUs5Gt8cy9_CmkmY6UA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-ORIG-GUID: abg4Ryfq43opm4tU6yzG9rDjiSF8_WmZ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjE5MDA4NiBTYWx0ZWRfX8w1vThKFGw0x KyA4fQtK/g03/5CYm8EI7zpFQ/9S1bOthfGT0O0vQa9HYUBGyW3IXWTGn7DFmin1Nnd5Jyp1yTL xTPY0spDLPo3NGTv221uWii0zPJSdzpetE19kOe+TFUladFNDjMhGQd5hnxHeVBbWWoJB3L7Ub4 9UfUR1Y8gIzmXlnwY1iNkSTeHw80bI8w0RV2LGemnGWiy1XuRkwRpCVC3LGu0a0Bd76tJlQxgfP 1NYDlyoFfbbiu8YIQYzTEcD0qNKkXftWGVeHkI0Is6qab8BCE6zwf4W8IrLG2I8OI/0+vGRRWSV FSmwmWB2T3g+z5zT+8XqxuTaq9/RtUsF4qapSnxqWg8uqmVNEfFC1VnyQtk9TB+RwxXvSKeR1YC f7mSHKkbrKr/3HbIZ2GWQIDZi+SivCcB6n+nHBm/U567BUlsCd/W25FqCXea2Fov7HvqZJI9YQx 73T05Zpl0yDyLWJfp4A== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-19_02,2026-06-18_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 impostorscore=0 malwarescore=0 adultscore=0 spamscore=0 bulkscore=0 priorityscore=1501 phishscore=0 clxscore=1011 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606190086 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 Applied, thanks!