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SubjectRe: [PATCH v3 0/6] clocksource: rework Atmel TCB timer driver
On 28/03/2018 at 16:36:34 +0200, Daniel Lezcano wrote:
> 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. März 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 ?
>

The core is giving deltas of 31 clocks instead of much more than that, I
guess I messed up the initialization somewhere.


--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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