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.
