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Subject: Re: [PATCH v3 0/6] clocksource: rework Atmel TCB timer driver
To:     Alexander Dahl <ada@thorsis.com>
Cc:     linux-arm-kernel@lists.infradead.org,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        linux-kernel@vger.kernel.org,
        Boris Brezillon <boris.brezillon@bootlin.com>,
        Thomas Gleixner <tglx@linutronix.de>
References: <20180223171558.7037-1-alexandre.belloni@bootlin.com>
 <9761072.pX2B0LJlSJ@ada> <989df8a3-462a-c645-87f1-9f956e1b22c9@linaro.org>
 <4073350.0MmxRoANOi@ada>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <6d43177a-bbea-6a01-5fa5-1c7891e18412@linaro.org>
Date:   Wed, 28 Mar 2018 15:03:11 +0200
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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.


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