linux-kernel - Re: High-resolution timers not supported when using smp

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Message-ID: <5543367E.5040807@free.fr>
Date:	Fri, 01 May 2015 10:17:02 +0200
From:	Mason <slash.tmp@...e.fr>
To:	John Stultz <john.stultz@...aro.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: High-resolution timers not supported when using smp_twd

Hello John,

On 30/04/2015 18:42, John Stultz wrote:

> On Thu, Apr 30, 2015 at 5:46 AM, Mason wrote:
>
>> I wanted to enable high-resolution timers on this Cortex A9 system,
>> but it seems there is more to it than just enabling
>>
>>   CONFIG_HIGH_RES_TIMERS=y
>>
>> (The system is limited to jiffy resolution.)
> 
> You might make sure you've got a HRT enabled clocksource installed?
> 
> You might check
> /sys/devices/system/clocksource/clocksource0/current_clocksource ?

Thanks for the suggestion, I will check on Monday.

The clocksource is a constant 27 MHz 32-bit counter.

It seems the problem comes from the clockevent source, which is
marked CLOCK_EVT_FEAT_C3STOP. If I remove that flag, then hrtimers
are enabled; but the flag is there for a good reason, I assume.

I will resend my message to the LAKML on Monday.

Regards.

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