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Date: Sun, 18 Nov 2018 03:17:17 +0100
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Vineet Gupta <vineet.gupta1@...opsys.com>,
Alexey Brodkin <alexey.brodkin@...opsys.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: "linux-snps-arc@...ts.infradead.org"
<linux-snps-arc@...ts.infradead.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] clocksource/drivers/arc_timer: Utilize generic
sched_clock
On 05/11/2018 15:39, Daniel Lezcano wrote:
> 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@...opsys.com>
>>> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
>>> Cc: Vineet Gupta <vgupta@...opsys.com>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> ---
>>
>> Acked-by: Vineet Gupta <vgupta@...opsys.com>
>>
>> @Daniel is this going via timer tree or you want me to pick it up.
>
> I will take care of it.
Please resend without the arch Kconfig change
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