From: Viresh Kumar <viresh.kumar@linaro.org>
To: vichy <vichy.kuo@gmail.com>
Cc: "cpufreq@vger.kernel.org" <cpufreq@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
Linux PM list <linux-pm@vger.kernel.org>
Subject: Re: about system time incorrect after changing cpu frequency
Date: Tue, 1 Sep 2015 13:12:05 +0530 [thread overview]
Message-ID: <20150901074205.GC1456@linux> (raw)
In-Reply-To: <CAOVJa8Hh0i05M7f39Pd9bXQmJA9n8tKTwNQoSmwAdUSSGtP_3w@mail.gmail.com>
On 01-09-15, 15:21, vichy wrote:
> and I add PLAT_gt_change_freq in arm_global_timer.c like below:
> PLAT_gt_change_freq calling() {
> gt_clk_rate = get_periph_clk();
> clockevents_update_freq(this_cpu_ptr(gt_evt), gt_clk_rate);
In earlier versions of kernel, this had a problem that it works only
for ONESHOT mode and simply returns in PERIODIC mode. I do see that
your's mode is ONESHOT only, and so it should have worked.
Anyway, few prints into that routine to see where we are reaching
might help.
> __clocksource_updatefreq_hz(>_clocksource, gt_clk_rate);
AFAIR, there is a difference between how different mdelay/udelay are
implemented. One of them is using the loops_per_jiffie variable to
calculate the time, other uses clkevt device. I am not 100% sure about
the theory, but that's what I remember. So, have a look from that
perspective as well..
--
viresh
WARNING: multiple messages have this Message-ID (diff)
From: viresh.kumar@linaro.org (Viresh Kumar)
To: linux-arm-kernel@lists.infradead.org
Subject: about system time incorrect after changing cpu frequency
Date: Tue, 1 Sep 2015 13:12:05 +0530 [thread overview]
Message-ID: <20150901074205.GC1456@linux> (raw)
In-Reply-To: <CAOVJa8Hh0i05M7f39Pd9bXQmJA9n8tKTwNQoSmwAdUSSGtP_3w@mail.gmail.com>
On 01-09-15, 15:21, vichy wrote:
> and I add PLAT_gt_change_freq in arm_global_timer.c like below:
> PLAT_gt_change_freq calling() {
> gt_clk_rate = get_periph_clk();
> clockevents_update_freq(this_cpu_ptr(gt_evt), gt_clk_rate);
In earlier versions of kernel, this had a problem that it works only
for ONESHOT mode and simply returns in PERIODIC mode. I do see that
your's mode is ONESHOT only, and so it should have worked.
Anyway, few prints into that routine to see where we are reaching
might help.
> __clocksource_updatefreq_hz(>_clocksource, gt_clk_rate);
AFAIR, there is a difference between how different mdelay/udelay are
implemented. One of them is using the loops_per_jiffie variable to
calculate the time, other uses clkevt device. I am not 100% sure about
the theory, but that's what I remember. So, have a look from that
perspective as well..
--
viresh
next prev parent reply other threads:[~2015-09-01 7:42 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
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 [this message]
2015-09-01 7:42 ` Viresh Kumar
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