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From: Jisheng Zhang <jszhang@marvell.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: vichy <vichy.kuo@gmail.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"cpufreq@vger.kernel.org" <cpufreq@vger.kernel.org>,
	Linux PM list <linux-pm@vger.kernel.org>
Subject: Re: about system time incorrect after changing cpu frequency
Date: Tue, 1 Sep 2015 14:39:23 +0800	[thread overview]
Message-ID: <20150901143923.11b075b5@xhacker> (raw)
In-Reply-To: <20150901060236.GB1456@linux>

On Tue, 1 Sep 2015 11:32:36 +0530
Viresh Kumar <viresh.kumar@linaro.org> wrote:

> On 01-09-15, 13:36, vichy wrote:
> > >> I try to call below 2 functions to change the frequency of clocksource
> > >> and clockevent, but the above b) sleep time is still incorrect when
> > >> cpu runs in 500Mhz.
> > >>     clockevents_update_freq(this_cpu_ptr(gt_evt), gt_clk_rate);
> > >>     __clocksource_updatefreq_hz(&gt_clocksource, gt_clk_rate);
> 
> How and when were you calling them? What kernel version is it ?
> 
> > Clock Event Device: arm_global_timer
> 
> This driver doesn't have support to update clkevt device's freq. You
> may need to modify that based on how arch/arm/kernel/smp_twd.c is
> updated. look for: clockevents_update_freq().
> 

This can only help the clockevent. Even with this cpufreq notifier
update, the globaltimer clocksource still can't hold correct/accurate time.

I think the arm global timer is not suitable for clocksource if cpufreq is
enabled.


WARNING: multiple messages have this Message-ID (diff)
From: jszhang@marvell.com (Jisheng Zhang)
To: linux-arm-kernel@lists.infradead.org
Subject: about system time incorrect after changing cpu frequency
Date: Tue, 1 Sep 2015 14:39:23 +0800	[thread overview]
Message-ID: <20150901143923.11b075b5@xhacker> (raw)
In-Reply-To: <20150901060236.GB1456@linux>

On Tue, 1 Sep 2015 11:32:36 +0530
Viresh Kumar <viresh.kumar@linaro.org> wrote:

> On 01-09-15, 13:36, vichy wrote:
> > >> I try to call below 2 functions to change the frequency of clocksource
> > >> and clockevent, but the above b) sleep time is still incorrect when
> > >> cpu runs in 500Mhz.
> > >>     clockevents_update_freq(this_cpu_ptr(gt_evt), gt_clk_rate);
> > >>     __clocksource_updatefreq_hz(&gt_clocksource, gt_clk_rate);
> 
> How and when were you calling them? What kernel version is it ?
> 
> > Clock Event Device: arm_global_timer
> 
> This driver doesn't have support to update clkevt device's freq. You
> may need to modify that based on how arch/arm/kernel/smp_twd.c is
> updated. look for: clockevents_update_freq().
> 

This can only help the clockevent. Even with this cpufreq notifier
update, the globaltimer clocksource still can't hold correct/accurate time.

I think the arm global timer is not suitable for clocksource if cpufreq is
enabled.

  reply	other threads:[~2015-09-01  6:39 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-08-31 14:03 about system time incorrect after changing cpu frequency vichy
2015-08-31 14:03 ` vichy
2015-09-01  3:57 ` Viresh Kumar
2015-09-01  3:57   ` Viresh Kumar
2015-09-01  5:36   ` vichy
2015-09-01  5:36     ` vichy
2015-09-01  6:02     ` Viresh Kumar
2015-09-01  6:02       ` Viresh Kumar
2015-09-01  6:39       ` Jisheng Zhang [this message]
2015-09-01  6:39         ` Jisheng Zhang
2015-09-01  7:37         ` vichy
2015-09-01  7:37           ` vichy
2015-09-01  7:21       ` vichy
2015-09-01  7:21         ` vichy
2015-09-01  7:42         ` Viresh Kumar
2015-09-01  7:42           ` Viresh Kumar

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