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-ow...@vger.kernel.org
[mailto:linux-kernel-ow...@vger.kernel.org] De la part de Dietmar Eggemann
Envoyé : mercredi 6 février 2019 11:55
À : Frédéric Mathieu <frederic.math...@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
...
[...]
