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SubjectRe: [PATCH v2] clocksource/drivers/arc_timer: Utilize generic sched_clock
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On 10/17/2018 04:30 AM, Alexey Brodkin wrote:
> It turned out we used to use default implementation of sched_clock()
> from kernel/sched/clock.c which was as precise as 1/HZ, i.e.
> by default we had 10 msec granularity of time measurement.
>
> Now given ARC built-in timers are clocked with the same frequency as
> CPU cores we may get much higher precision of time tracking.
>
> Thus we switch to generic sched_clock which really reads ARC hardware
> counters.
>
> This is especially helpful for measuring short events.
> That's what we used to have:
> ------------------------------>8------------------------
> $ perf stat /bin/sh -c /root/lmbench-master/bin/arc/hello > /dev/null
>
> Performance counter stats for '/bin/sh -c /root/lmbench-master/bin/arc/hello':
>
> 10.000000 task-clock (msec) # 2.832 CPUs utilized
> 1 context-switches # 0.100 K/sec
> 1 cpu-migrations # 0.100 K/sec
> 63 page-faults # 0.006 M/sec
> 3049480 cycles # 0.305 GHz
> 1091259 instructions # 0.36 insn per cycle
> 256828 branches # 25.683 M/sec
> 27026 branch-misses # 10.52% of all branches
>
> 0.003530687 seconds time elapsed
>
> 0.000000000 seconds user
> 0.010000000 seconds sys
> ------------------------------>8------------------------
>
> And now we'll see:
> ------------------------------>8------------------------
> $ perf stat /bin/sh -c /root/lmbench-master/bin/arc/hello > /dev/null
>
> Performance counter stats for '/bin/sh -c /root/lmbench-master/bin/arc/hello':
>
> 3.004322 task-clock (msec) # 0.865 CPUs utilized
> 1 context-switches # 0.333 K/sec
> 1 cpu-migrations # 0.333 K/sec
> 63 page-faults # 0.021 M/sec
> 2986734 cycles # 0.994 GHz
> 1087466 instructions # 0.36 insn per cycle
> 255209 branches # 84.947 M/sec
> 26002 branch-misses # 10.19% of all branches
>
> 0.003474829 seconds time elapsed
>
> 0.003519000 seconds user
> 0.000000000 seconds sys
> ------------------------------>8------------------------
>
> Note how much more meaningful is the second output - time spent for
> execution pretty much matches number of cycles spent (we're running
> @ 1GHz here).
>
> Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Vineet Gupta <vgupta@synopsys.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---

Acked-by: Vineet Gupta <vgupta@synopsys.com>

@Daniel is this going via timer tree or you want me to pick it up.

Thx,
-Vineet


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