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

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Message-ID: <3478710.yJBBt3uoRT@ada>
Date:   Thu, 29 Mar 2018 10:01:26 +0200
From:   Alexander Dahl <ada@...rsis.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 0/6] clocksource: rework Atmel TCB timer driver

Hei hei,

Am Mittwoch, 28. März 2018, 17:50:33 CEST schrieb Alexandre Belloni:
> On 28/03/2018 at 17:31:35 +0200, Alexandre Belloni wrote:
> > > 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.
> 
> I did mess up.
> 
> Alexander, can you test that:

Well, I just did.

> 
> diff --git a/drivers/clocksource/timer-atmel-tcb.c
> b/drivers/clocksource/timer-atmel-tcb.c index 7fde9cfbf203..bbbacf8c46b0
> 100644
> --- a/drivers/clocksource/timer-atmel-tcb.c
> +++ b/drivers/clocksource/timer-atmel-tcb.c
> @@ -222,7 +222,7 @@ static int __init tc_clkevt_register(struct device_node
> *node, goto err_slow;
>  	clk_disable(tce.clk);
> 
> -	clockevents_config_and_register(&tce.clkevt, 32768, 1, bits - 1);
> +	clockevents_config_and_register(&tce.clkevt, 32768, 1, BIT(bits) - 1);
> 
>  	ret = request_irq(tce.irq, tc_clkevt2_irq, IRQF_TIMER | IRQF_SHARED,
>  			  tce.clkevt.name, &tce);
> 
> This will behave exactly the same as before on 16bits TCB and will have
> much less interrupts on 32 bits platforms.

This is the result:

INT                NAME          RATE             MAX
 17 [vel     timer@...a]  1837 Ints/s     (max:  1912)
 26 [      vel     eth0]     3 Ints/s     (max:    11)

This is not much lower than the ~2150 I reported yesterday?

I'm sorry I can just test this on at91sam9g20 currently, I have no 
understanding of the subsystem, I can't do a decent review.

Greets
Alex