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SubjectRe: [PATCH v2] clocksource/drivers/arc_timer: Utilize generic sched_clock
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On 24/10/2018 00:33, Vineet Gupta wrote:
> 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.

Applied, thanks

-- Daniel

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