[PATCH v8 4/6] clocksource: stm32: only use 32 bits timers

On 07/12/2017 21:36, Benjamin Gaignard wrote:

2017-12-07 17:49 GMT+01:00 Daniel Lezcano [off-list ref]:

quoted

On 07/12/2017 17:33, Benjamin Gaignard wrote:

quoted

2017-12-07 16:27 GMT+01:00 Daniel Lezcano [off-list ref]:

quoted

On 14/11/2017 09:52, Benjamin Gaignard wrote:

quoted

The clock driving counters is at 90MHz so the maximum period
for 16 bis counters is around 750 ms which is a short period
for a clocksource.

Isn't it 728us ?

yes it is: 2^16 / 90.000.000 => 728us

Ok, now I can do the connection with the previous patch.

So, the real issue of all this is the 16bits clocksource is wrapping up
every 728us, hence the clockevent periodically expires every ~728us to
keep the timekeeping consistent. Unfortunately, the kernel has a too
high overhead for this as the system is consistently processing this
timer leading to a CPU time resource starvation.

Is that correct ?

Yes that is correct

Oh man. That was unclear since the beginning, we are not talking about
inaccurate clocksource or whatever but just these 16bits timers can't
work on Linux.


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