linux-kernel - Re: [PATCH v2] clocksource/drivers/arc_timer: Utilize generic sched

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Message-ID: <2c46ab6e-f0a9-4857-9772-f3c714284e98@linaro.org>
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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