Messages in this thread | | | Subject | Re: Kernel 4.9: strange behavior with fifo scheduler | From | Dietmar Eggemann <> | Date | Thu, 7 Feb 2019 12:27:08 +0100 |
| |
On 2/6/19 2:25 PM, Frédéric Mathieu wrote: > Hi Dietmar, > > Attention !, these tests were executed on a kernel with the patch RT and the option CONFIG_PREEMPT_RT_FULL = y. I confirm the truth of my priority settings > On a vanilla kernel, I get the same results as you. > > After talking with mike Galbraith, I turned my attention to the priority of kernel threads. The following link explains in the behavior of the scheduler : > https://wiki.linuxfoundation.org/realtime/documentation/technical_details/hr_timers > > Contrary to what I thought, there is no dynamic adjustment of the priority according to the priority of the calling task. > > -----Message d'origine----- > De : linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] De la part de Dietmar Eggemann > Envoyé : mercredi 6 février 2019 11:55 > À : Frédéric Mathieu <frederic.mathieu@dualis.com>; linux-kernel@vger.kernel.org > Objet : Re: Kernel 4.9: strange behavior with fifo scheduler > > Hi Frédéric, > > On 2/5/19 11:47 AM, Frédéric Mathieu wrote: >> Hi, >> >> on an X86_64 architecture (Intel(R) Core(TM) i3-6100U CPU @ 2.30GHz), >> I use the linux kernel 4.9.146 with patch rt 125. >> uname -a: Linux 4.9.146-rt125 #1 SMP PREEMPT RT Tue Jan 29 14:17:55 >> CET 2019 >> x86_64 GNU/Linux
Ah, OK, I should have read it more carefully! So you're talking about the ktimersoftd/0 thread in this case which makes cyclictest show the latency of ~6ms every 5th time.
v4.9 + rt 125 on ARM64 Juno: (test prio (49) > cyclictest prio (50)
... ktimersoftd/0-4 [000] 54.948862: sched_pi_setprio: comm=ktimersoftd/0 pid=4 oldprio=49 newprio=98 ktimersoftd/0-4 [000] 54.948867: sched_waking: comm=cyclictest pid=2730 prio=49 target_cpu=000 ktimersoftd/0-4 [000] 54.948870: sched_wakeup: cyclictest:2730 [49] success=1 CPU:000 ktimersoftd/0-4 [000] 54.948874: sched_switch: ktimersoftd/0:4 [98] R ==> cyclictest:2730 [49] cyclictest-2730 [000] 54.948890: sched_switch: cyclictest:2730 [49] S ==> ktimersoftd/0:4 [98] ktimersoftd/0-4 [000] 54.948906: sched_switch: ktimersoftd/0:4 [98] S ==> swapper/0:0 [120] <idle>-0 [000] 54.949087: sched_waking: comm=test pid=2723 prio=50 target_cpu=000 <idle>-0 [000] 54.949090: sched_wakeup: test:2723 [50] success=1 CPU:000 <idle>-0 [000] 54.949098: sched_switch: swapper/0:0 [120] R ==> test:2723 [50] test-2723 [000] 54.949784: sched_waking: comm=ktimersoftd/0 pid=4 prio=98 target_cpu=000 test-2723 [000] 54.949787: sched_wakeup: ktimersoftd/0:4 [98] success=1 CPU:000 test-2723 [000] 54.951979: sched_waking: comm=ksoftirqd/0 pid=3 prio=120 target_cpu=000 test-2723 [000] 54.951983: sched_wakeup: ksoftirqd/0:3 [120] success=1 CPU:000 test-2723 [000] 54.955111: sched_switch: test:2723 [50] S ==> ktimersoftd/0:4 [98] ktimersoftd/0-4 [000] 54.955125: sched_waking: comm=cyclictest pid=2730 prio=49 target_cpu=000 ktimersoftd/0-4 [000] 54.955128: sched_wakeup: cyclictest:2730 [49] success=1 CPU:000 ktimersoftd/0-4 [000] 54.955132: sched_switch: ktimersoftd/0:4 [98] R ==> cyclictest:2730 [49] cyclictest-2730 [000] 54.955138: sched_pi_setprio: comm=ktimersoftd/0 pid=4 oldprio=98 newprio=49 cyclictest-2730 [000] 54.955145: sched_switch: cyclictest:2730 [49] D ==> ktimersoftd/0:4 [49] ktimersoftd/0-4 [000] 54.955149: sched_pi_setprio: comm=ktimersoftd/0 pid=4 oldprio=49 newprio=98 ktimersoftd/0-4 [000] 54.955154: sched_waking: comm=cyclictest pid=2730 prio=49 target_cpu=000 ktimersoftd/0-4 [000] 54.955157: sched_wakeup: cyclictest:2730 [49] success=1 CPU:000 ...
[...]
| |