Re: [RFC PATCH V0 09/10] trace/kmmscand: Add tracing of scanning and migration

[Steven Rostedt]

On Fri, 6 Dec 2024 12:03:29 +0530
Raghavendra K T <raghavendra.kt@xxxxxxx> wrote:

> On 12/5/2024 11:16 PM, Steven Rostedt wrote:
> > On Sun, 1 Dec 2024 15:38:17 +0000
> > Raghavendra K T <raghavendra.kt@xxxxxxx> wrote:
> >   
> >> Add tracing support to track
> >>   - start and end of scanning.
> >>   - migration.
> >>
> >> CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
> >> CC: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> >> CC: linux-trace-kernel@xxxxxxxxxxxxxxx
> >>  
> 
> [...]
> 
> >> +
> >> +	TP_STRUCT__entry(
> >> +		__array(	char, comm, TASK_COMM_LEN	)  
> > 
> > Is there a reason to record "comm"? There's other ways to retrieve it than
> > to always write it to the ring buffer.
> >   
> 
> Thank you for the review Steve. The motivation was to filter benchmark
> in the trace to understand the behavior.
> I will explore regarding other ways of retrieving comm.
> (or may be even PID is enough..)

You can filter on current comm for any event with trace-cmd and even with the
"filter" file. It doesn't need to be part of the event.

For the filter file:

 # echo "COMM == rcu_preempt" > /sys/kernel/tracing/events/timer/hrtimer_cancel/filter

or with trace-cmd

 # trace-cmd start -e hrtimer_cancel -f 'COMM == "rcu_preempt"'
 # trace-cmd show
# tracer: nop
#
# entries-in-buffer/entries-written: 10/10   #P:8
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
     rcu_preempt-18      [001] d..3. 54968.170887: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54968.177704: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54968.181678: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54968.185679: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54968.186092: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54968.193676: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54968.193686: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54972.871315: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54972.875176: hrtimer_cancel: hrtimer=00000000456b5702
     rcu_preempt-18      [001] d..3. 54972.881751: hrtimer_cancel: hrtimer=00000000456b5702

Or you can do it after the fact from a trace.dat file:

  # trace-cmd record -e hrtimer_cancel sleep 10
  # trace-cmd report | head
cpus=8
           sleep-1641  [006] d.h2. 55109.598846: hrtimer_cancel:       hrtimer=0xffff9800fdfa1888
           sleep-1641  [006] d..3. 55109.599089: hrtimer_cancel:       hrtimer=0xffff9800fdfb3140
          <idle>-0     [006] d..2. 55109.599111: hrtimer_cancel:       hrtimer=0xffff9800fdfa1888
          <idle>-0     [006] d.h7. 55109.603848: hrtimer_cancel:       hrtimer=0xffff9800fdfb3180
          <idle>-0     [006] dN.2. 55109.603895: hrtimer_cancel:       hrtimer=0xffff9800fdfa1888
          <idle>-0     [000] d.h3. 55109.604478: hrtimer_cancel:       hrtimer=0xffff9800fde33180
          <idle>-0     [000] dN.2. 55109.604492: hrtimer_cancel:       hrtimer=0xffff9800fde21888
     rcu_preempt-18    [000] d..3. 55109.604549: hrtimer_cancel:       hrtimer=0xffff9800fde33140
          <idle>-0     [000] d..2. 55109.604573: hrtimer_cancel:       hrtimer=0xffff9800fde21888

  # trace-cmd report -F '.*:COMM == "rcu_preempt"'
cpus=8
     rcu_preempt-18    [000] d..3. 55109.604549: hrtimer_cancel:       hrtimer=0xffff9800fde33140
     rcu_preempt-18    [000] d..3. 55109.609320: hrtimer_cancel:       hrtimer=0xffff9800fde33140
     rcu_preempt-18    [000] d..3. 55109.613350: hrtimer_cancel:       hrtimer=0xffff9800fde33140
     rcu_preempt-18    [000] d..3. 55119.609772: hrtimer_cancel:       hrtimer=0xffff9800fde33140

-- Steve