schedule latency on am335x board

yuri exi

Intellectual 865 points

Hi all

I tested kernel latency by tracer

I used to ti-sdk-am335x-evm-08.00.00.00 on am335x board

The Wonder common problems that occur in a typical idle state

Do you have ways to improve latency?

Is this latencie inherent to classic Linux?

# wakeup latency trace v1.1.5 on 3.14.26-rt25-g07d13c6-dirty
# --------------------------------------------------------------------
# latency: 59 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
#    -----------------
#    | task: rcuc/0-13 (uid:0 nice:0 policy:1 rt_prio:1)
#    -----------------
#
#                   _--------=> CPU#
#                  / _-------=> irqs-off
#                 | / _------=> need-resched
#                 || / _-----=> need-resched_lazy
#                 ||| / _----=> hardirq/softirq
#                 |||| / _---=> preempt-depth
#                 ||||| / _--=> preempt-lazy-depth
#                 |||||| / _-=> migrate-disable
#                 ||||||| /     delay
# cmd     pid    |||||||| time |   caller
#     \   /      |||||||| \   |   /
<idle>-0       0dn.h4..    4us+:      0:120:R   + [000]    13: 98:S rcuc/0
<idle>-0       0dn.h4..   17us+: try_to_wake_up <-wake_up_process
<idle>-0       0d...3..   55us+: __schedule <-schedule
<idle>-0       0d...3..   57us :      0:120:R ==> [000]    13: 98:R rcuc/0

# wakeup latency trace v1.1.5 on 3.14.26-rt25-g07d13c6-dirty
# --------------------------------------------------------------------
# latency: 57 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
#    -----------------
#    | task: irq/88-OMAP UAR-897 (uid:0 nice:0 policy:1 rt_prio:50)
#    -----------------
#
#                   _--------=> CPU#
#                  / _-------=> irqs-off
#                 | / _------=> need-resched
#                 || / _-----=> need-resched_lazy
#                 ||| / _----=> hardirq/softirq
#                 |||| / _---=> preempt-depth
#                 ||||| / _--=> preempt-lazy-depth
#                 |||||| / _-=> migrate-disable
#                 ||||||| /     delay
# cmd     pid    |||||||| time |   caller
#     \   /      |||||||| \   |   /
      sh-1607    0dn.h3..    5us+:   1607:120:S   + [000]   897: 49:S irq/88-OMAP UAR
      sh-1607    0dn.h3..   24us+: try_to_wake_up <-wake_up_process
      sh-1607    0d...3..   51us+: __schedule <-preempt_schedule_irq
      sh-1607    0d...3..   54us :   1607:120:S ==> [000]   897: 49:R irq/88-OMAP UAR

# tracer: wakeup_rt
#
# wakeup_rt latency trace v1.1.5 on 3.14.26-rt25-g07d13c6-dirty
# --------------------------------------------------------------------
# latency: 59 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
#    -----------------
#    | task: irq/57-4a100000-879 (uid:0 nice:0 policy:1 rt_prio:50)
#    -----------------
#
#                   _--------=> CPU#
#                  / _-------=> irqs-off
#                 | / _------=> need-resched
#                 || / _-----=> need-resched_lazy
#                 ||| / _----=> hardirq/softirq
#                 |||| / _---=> preempt-depth
#                 ||||| / _--=> preempt-lazy-depth
#                 |||||| / _-=> migrate-disable
#                 ||||||| /     delay
# cmd     pid    |||||||| time |   caller
#     \   /      |||||||| \   |   /
<idle>-0       0dn.h4..    5us+:      0:120:R   + [000]   879: 49:S irq/57-4a100000
<idle>-0       0dn.h4..   17us+: try_to_wake_up <-wake_up_process
<idle>-0       0d...3..   54us+: __schedule <-schedule
<idle>-0       0d...3..   56us :      0:120:R ==> [000]   879: 49:R irq/57-4a100000
root@am335x-evm:/sys/kernel/debug/tracing#

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Realtime kernels are currently not supported on AM335X. You can find wakeup latencies information here: processors.wiki.ti.com/.../Processor_SDK_Linux_Kernel_Performance_Guide

0 yuri exi over 9 years ago in reply to Biser Gatchev-XID

Intellectual 865 points

I fully understand your answers.

Thank you

I have another question about schedule latency.

looking at the above tracer result.

<idle>-0 0dn.h4.. 17us+: try_to_wake_up <-wake_up_process
<idle>-0 0d...3.. 55us+: __schedule <-schedule

always Appears in tracer result.

I know, try_to_wake_up is wake up a thread.

thread always entering sleep mode(or idle mode)?

can I disable thread sleep mode(or idle mode)?

If I can disable thread sleep mode(or idle mode), How can I disable sleep mode(or idle mode)?

thank you always for your support.

0 Biser Gatchev-XID over 9 years ago in reply to yuri exi

TI__Guru**** 393215 points

I have asked the software team to help on your last questions.

0 Yordan Kovachev over 9 years ago in reply to yuri exi

TI__Guru**** 161600 points

Hi,

I don't see a handle to disable sleep/idle of the try_to_wake_up() function globally (it doesn't seem to have such state). Moreover this call is used to wake up another process, it is called by sched every time, when process needs to be woken up.

"If I can disable thread sleep mode(or idle mode), How can I disable sleep mode(or idle mode)?"
Have you tried to disable the runtime pm of the kernel?

Best Regards,
Yordan

0 yuri exi over 9 years ago in reply to Yordan Kovachev

Intellectual 865 points

thank you so much
I solved my problem~!!!!!

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schedule latency on am335x board