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Tue, 20 Jan 2026 12:42:08 +0000 (GMT) Message-ID: Date: Tue, 20 Jan 2026 18:12:08 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/15] tick/sched: Refactor idle cputime accounting To: Frederic Weisbecker , LKML Cc: "Rafael J . Wysocki" , Boqun Feng , Thomas Gleixner , Steven Rostedt , "Christophe Leroy (CS GROUP)" , Kieran Bingham , Ben Segall , Michael Ellerman , Ingo Molnar , Vincent Guittot , Juri Lelli , Neeraj Upadhyay , Xin Zhao , Madhavan Srinivasan , Mel Gorman , Valentin Schneider , Christian Borntraeger , Jan Kiszka , linuxppc-dev@lists.ozlabs.org, "Paul E . McKenney" , Viresh Kumar , Anna-Maria Behnsen , Uladzislau Rezki , Dietmar Eggemann , Heiko Carstens , linux-pm@vger.kernel.org, Alexander Gordeev , Sven Schnelle , Vasily Gorbik , Joel Fernandes , Nicholas Piggin , linux-s390@vger.kernel.org, Peter Zijlstra References: <20260116145208.87445-1-frederic@kernel.org> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 9VV4fpwLWP4PF7lZThEunm4rJxceXtvg X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTIwMDEwMiBTYWx0ZWRfXx9yKJqyysrW6 O/oFmXr8RITUzlMs5DnwBfn5ZTKL+8h6NXFtpi2UTke7YxOrw8thQeRvFH1Rqw/buSAqehlaesH nHkvyGOjnOPcbxQ0RedRbvPpZErqOlolFyjPwFZuw0OWJkuKqgvLPcqtC4kSS4X+cJxhYzBRkp/ XnJk0Lypiae2n00EVXJV42JlQ1FJyASmG26LSchKXjRntd6qlJr1c6gSSw5RP+e9WK8va47/EC8 JiRCrB9ruCncX7lC5AmMr8ff/5fj+3JgzCarsyq+Yj3AtVOG8kHn8SE26/AoSixmgtANzoseJ6E vwtwRXROIg8svyoC+arO4xzyzRousjDjafz2VyQ/6ztbnbQBV5mVIHW70HHcgLh0W5FW3oIyVX9 qPURUSaTIo+rO5pT60kuxPZF0baSr0nQnBThZy6pw6ip5owcY+UTLBqKwIskNeyMtSH6C40GGKu Jqvps5z2AAIMS4bCkPg== X-Authority-Analysis: v=2.4 cv=J9SnLQnS c=1 sm=1 tr=0 ts=696f782e cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=if_OGZEsJgfgBzv6FlkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: xGI-wI0OTynA7CpsDBMAgvCg4UMlutJg X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.20,FMLib:17.12.100.49 definitions=2026-01-20_03,2026-01-20_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=0 adultscore=0 suspectscore=0 spamscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1011 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2601150000 definitions=main-2601200102 Hi Frederic. On 1/16/26 8:27 PM, Frederic Weisbecker wrote: > I forgot to mention I haven't yet tested CONFIG_VIRT_CPU_ACCOUNTING_NATIVE > (s390 and powerpc). > > Thanks. tl;dr I ran this on powerNV(Non virtualized) with 144 CPUs with below config. (default ones) Patch *breaks* the cpu idle stats most of the time. idle values are wrong. Detailed info: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ In config i have this: CONFIG_TICK_CPU_ACCOUNTING=y # CONFIG_VIRT_CPU_ACCOUNTING_NATIVE is not set # CONFIG_VIRT_CPU_ACCOUNTING_GEN is not set # CONFIG_IRQ_TIME_ACCOUNTING is not set # CONFIG_BSD_PROCESS_ACCT is not set +++++++++ When system is fully idle, i see this. 06:44:26 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 06:44:27 AM all 0.01 0.00 0.01 0.00 57.20 0.00 0.00 0.00 0.00 42.79 06:44:28 AM all 0.02 0.00 0.03 0.00 55.73 0.00 0.00 0.00 0.00 44.22 06:44:29 AM all 0.01 0.00 0.00 0.00 56.23 0.00 0.00 0.00 0.00 43.77 - Seeing 50%+ in irq time, which is clearly wrong. +++++++++ When running stress-ng --cpu=72 (expectation is 50% idle time) 06:48:12 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 06:48:13 AM all 49.98 0.00 0.01 0.00 15.81 0.00 0.00 0.00 0.00 34.20 06:48:14 AM all 49.93 0.00 0.00 0.00 15.15 0.00 0.00 0.00 0.00 34.91 06:48:15 AM all 49.99 0.00 0.01 0.00 15.29 0.00 0.00 0.00 0.00 34.72 - Wrong values again. 50% is expected idle time. +++++++++ system is idle again. 06:48:46 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 06:48:47 AM all 0.00 0.00 0.00 0.00 63.93 0.00 0.00 0.00 0.00 36.07 06:48:48 AM all 0.02 0.00 0.00 0.00 63.78 0.01 0.00 0.00 0.00 36.18 06:48:49 AM all 0.00 0.00 0.00 0.00 63.77 0.00 0.00 0.00 0.00 36.23 - Wrong values again. irq increased further. +++++++++ I have seen the below warnings too. WARNING: kernel/time/tick-sched.c:1353 at tick_nohz_idle_exit [ T0] WARNING: kernel/time/tick-sched.c:1353 at tick_nohz_idle_exit+0x148/0x150, CPU#4: swapper/4/0 [ T0] Modules linked in: vmx_crypto gf128mul [ T0] CPU: 4 UID: 0 PID: 0 Comm: swapper/4 Tainted: G W 6.19.0-rc5-00683-gbe7e8f3d5116 #61 PREEMPT(full) [ T0] Tainted: [W]=WARN [ T0] Hardware name: 0000000000000000 POWER9 0x4e1202 opal:v7.1 PowerNV [ T0] NIP [c0000000002c8210] tick_nohz_idle_exit+0x148/0x150 [ T0] LR [c00000000022f10c] do_idle+0x1dc/0x328 WARNING: kernel/time/tick-sched.c:1274 at tick_nohz_get_sleep_length T0] NIP [c0000000002c7fc0] tick_nohz_get_sleep_length+0x108/0x110 [ T0] LR [c000000000ca1548] menu_select+0x3c0/0x7b4 [ T0] Call Trace: [ T0] [c000000003197e10] [c000000003197e50] 0xc000000003197e50 (unreliable) [ T0] [c000000003197e50] [c000000000ca1548] menu_select+0x3c0/0x7b4 [ T0] [c000000003197ed0] [c000000000c9f120] cpuidle_select+0x34/0x48 [ T0] [c000000003197ef0] [c00000000022f184] do_idle+0x254/0x328 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ I went back to baseline to confirm the original behaviour. (d613f96096e4) Merge timers/vdso into tip/master 07:02:17 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 07:02:18 AM all 0.01 0.00 0.01 0.01 1.19 0.00 0.00 0.00 0.00 98.77 07:02:19 AM all 0.01 0.00 0.01 0.00 0.84 0.00 0.00 0.00 0.00 99.14 07:02:20 AM all 0.00 0.00 0.01 0.00 0.99 0.00 0.00 0.00 0.00 99.00 07:02:21 AM all 0.01 0.00 0.00 0.00 0.83 0.00 0.00 0.00 0.00 99.16 Which is the working as expected. PS: Initial data. I haven't gone through the series yet.