Re: Observation on NOHZ_FULL

[Uladzislau Rezki <urezki@gmail.com>]

> >>
> >> I have done some basic research about hrtimer_interrupt() latency on my
> >> HW with latest Linux kernel. I have compared below cases:
> >>
> >> case a: 1000HZ + lazy + nocb_all_cpus
> >> case b: 1000HZ + nocb_all_cpus
> >>
> >> I used "ftrace" to measure time(in microseconds). Steps:
> >>
> >> echo 0 > tracing_on
> >> echo function_graph > current_tracer
> >> echo funcgraph-proc > trace_options
> >> echo funcgraph-abstime > trace_options
> >> echo hrtimer_interrupt > set_ftrace_filter
> >>
> >> fio --rw=write --bs=1M --size=1G --numjobs=8 --name=worker --time_based --runtime=50&
> >>
> >> echo 1 > tracing_on; sleep 10; echo 0 > tracing_on
> >>
> >> data is based on 10 seconds collection:
> >>
> >> <case a>
> >>      6  2102 ############################################################
> >>      8  2079 ############################################################
> >>     10  1464 ##########################################
> >>      7   897 ##########################
> 
> So first column is microseconds and second one is count?
> 
Right!

> >>      9   625 ##################
> >>     12   490 ##############
> >>     13   479 ##############
> >>     11   289 #########
> >>      5   249 ########
> >>     14   124 ####
> >>     15    72 ###
> >>     16    41 ##
> >>     17    24 #
> >>      4    22 #
> >>     18    12 #
> >>     22     2 #
> >>     19     1 #
> >> <case a>
> >>
> >> <case b>
> >>      9  1658 ############################################################
> >>     13  1308 ################################################
> >>     12  1224 #############################################
> 
> Assuming that, it does seem the "best" case is off by 3 microseconds (9 vs 6),
> still would not warrant being regarded a bug and possibly just in the noise.
> 
I also think it is a noise.