linux-kernel - Re: [PATCH v2 18/20] mips: csrc-r4k: Decrease r4k-clocksource rating if CPU

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Date:   Fri, 8 May 2020 17:41:50 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Sergey.Semin@...kalelectronics.ru
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 18/20] mips: csrc-r4k: Decrease r4k-clocksource rating
 if CPU_FREQ enabled

On Wed, May 06, 2020 at 08:42:36PM +0300, Sergey.Semin@...kalelectronics.ru wrote:
> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> Commit 07d69579e7fe ("MIPS: Don't register r4k sched clock when
> CPUFREQ enabled") disabled the r4k-clock usage for scheduler ticks
> counting due to the scheduler being non-tolerant for unstable
> clocks sources. For the same reason the clock should be used
> in the system clocksource framework only as a last resort if CPU
> frequency may change.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Paul Burton <paulburton@...nel.org>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: linux-pm@...r.kernel.org
> Cc: devicetree@...r.kernel.org
> ---
>  arch/mips/kernel/csrc-r4k.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
> index 437dda64fd7a..d81fb374f477 100644
> --- a/arch/mips/kernel/csrc-r4k.c
> +++ b/arch/mips/kernel/csrc-r4k.c
> @@ -71,7 +71,11 @@ int __init init_r4k_clocksource(void)
>  		return -ENXIO;
>  
>  	/* Calculate a somewhat reasonable rating value */
> +#ifndef CONFIG_CPU_FREQ
>  	clocksource_mips.rating = 200 + mips_hpt_frequency / 10000000;
> +#else
> +	clocksource_mips.rating = 99;
> +#endif

I dislike this patch. Assuming you have an other clocksource, why not
simply disable csrc-r4k, if CPU_FREQ is enabled ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]