Re: [PATCH v3 0/6] clocksource: rework Atmel TCB timer driver

[Daniel Lezcano]

On 28/03/2018 16:16, Alexandre Belloni wrote:
> On 28/03/2018 at 15:03:11 +0200, Daniel Lezcano wrote:
>> On 28/03/2018 12:29, Alexander Dahl wrote:
>>> Hello Daniel,
>>>
>>> Am Dienstag, 27. MÃrz 2018, 13:30:22 CEST schrieb Daniel Lezcano:
>>>> Can you can give a rough amount for the irq rate on the timer ?
>>>
>>> I used itop [1] now to get a rough estimate. First with kernel v4.14.29-rt25 
>>> (fully preempt RT):
>>>
>>> INT                NAME          RATE             MAX
>>>  19 [ vel     tc_clkevt]   397 Ints/s     (max:   432)
>>>  26 [      vel     eth0]     4 Ints/s     (max:    38)
>>>
>>> Next test with kernel v4.15.13 gives (slightly slower, but non-RT):
>>>
>>> INT                NAME          RATE             MAX
>>>  19 [ vel     tc_clkevt]   248 Ints/s     (max:   273)
>>>  26 [      vel     eth0]     4 Ints/s     (max:    11)
>>>
>>> With kernel v4.16-rc7 plus this patch series and tcb as clocksource:
>>>
>>> INT                NAME          RATE             MAX
>>>  17 [vel     timer@fffa]  2164 Ints/s     (max:  2183)
>>>  26 [      vel     eth0]     5 Ints/s     (max:    10)
>>>
>>> Is this the information you wanted? If not, could you point me on how to get 
>>> the requested irq rate?
>>
>> It is perfect. Thanks!
>>
>> It confirms what I was worried about: the clocksource wraps up too
>> quickly thus raising an interrupt every 400us. That is why I asked
>> Alexande about a prescalar register.
>>
> 
> The code should behave exactly the same between the previous and the new
> driver. The interrupt is not coming from the clocksource but from the
> clockevent and it is already on the slowest clock, the 32kHz one.

Do you have an explanation of why the rate is much higher ?


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