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CPU is active when have running tasks on it and CPUFreq governor can
select different operating points (OPP) according to different workload;
we use 'pstate' to present CPU state which have running tasks with one
specific OPP. On the other hand, CPU is idle which only idle task on
it, CPUIdle governor can select one specific idle state to power off
hardware logics; we use 'cstate' to present CPU idle state.
Based on trace events 'cpu_idle' and 'cpu_frequency' we can accomplish
the duration statistics for every state. Every time when CPU enters
into or exits from idle states, the trace event 'cpu_idle' is recorded;
trace event 'cpu_frequency' records the event for CPU OPP changing, so
it's easily to know how long time the CPU stays in the specified OPP,
and the CPU must be not in any idle state.
This patch is to utilize the mentioned trace events for pstate and
cstate statistics. To achieve more accurate profiling data, the program
uses below sequence to insure CPU running/idle time aren't missed:
- Before profiling the user space program wakes up all CPUs for once, so
can avoid to missing account time for CPU staying in idle state for
long time; the program forces to set 'scaling_max_freq' to lowest
frequency and then restore 'scaling_max_freq' to highest frequency,
this can ensure the frequency to be set to lowest frequency and later
after start to run workload the frequency can be easily to be changed
to higher frequency;
- User space program reads map data and update statistics for every 5s,
so this is same with other sample bpf programs for avoiding big
overload introduced by bpf program self;
- When send signal to terminate program, the signal handler wakes up
all CPUs, set lowest frequency and restore highest frequency to
'scaling_max_freq'; this is exactly same with the first step so
avoid to missing account CPU pstate and cstate time during last
stage. Finally it reports the latest statistics.
The program has been tested on Hikey board with octa CA53 CPUs, below
is one example for statistics result, the format mainly follows up
Jesper Dangaard Brouer suggestion.
Jesper reminds to 'get printf to pretty print with thousands separators
use %' and setlocale(LC_NUMERIC, "en_US")', tried three different arm64
GCC toolchains (5.4.0 20160609, 6.2.1 20161016, 6.3.0 20170516) but all
of them cannot support printf flag character %' on arm64 platform, so go
back print number without grouping mode.
CPU states statistics:
state(ms) cstate-0 cstate-1 cstate-2 pstate-0 pstate-1 pstate-2 pstate-3 pstate-4
CPU-0 767 6111 111863 561 31 756 853 190
CPU-1 241 10606 107956 484 125 646 990 85
CPU-2 413 19721 98735 636 84 696 757 89
CPU-3 84 11711 79989 17516 909 4811 5773 341
CPU-4 152 19610 98229 444 53 649 708 1283
CPU-5 185 8781 108697 666 91 671 677 1365
CPU-6 157 21964 95825 581 67 566 684 1284
CPU-7 125 15238 102704 398 20 665 786 1197
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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