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From: Dmitry Osipenko <digetx@gmail.com>
To: Chanwoo Choi <cw00.choi@samsung.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	MyungJoo Ham <myungjoo.ham@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>,
	linux-pm@vger.kernel.org, linux-tegra@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 08/19] PM / devfreq: tegra30: Ensure that target freq won't overflow
Date: Wed, 21 Aug 2019 02:19:52 +0300
Message-ID: <f4398556-12e0-9ba8-b59b-19a38764312f@gmail.com> (raw)
In-Reply-To: <c85dbd27-7536-9c51-19a2-fe1c2c6342b9@samsung.com>

Hello Chanwoo,

20.08.2019 3:23, Chanwoo Choi пишет:
> On 19. 8. 12. 오전 6:23, Dmitry Osipenko wrote:
>> We already had few integer overflow bugs, let's limit the freq for
>> consistency.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>> ---
>>  drivers/devfreq/tegra30-devfreq.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/devfreq/tegra30-devfreq.c b/drivers/devfreq/tegra30-devfreq.c
>> index 70dce58212a4..ca499368ee81 100644
>> --- a/drivers/devfreq/tegra30-devfreq.c
>> +++ b/drivers/devfreq/tegra30-devfreq.c
>> @@ -430,7 +430,7 @@ static unsigned long actmon_update_target(struct tegra_devfreq *tegra,
>>  	target_freq = dev->avg_count / ACTMON_SAMPLING_PERIOD + dev->boost_freq;
>>  	target_freq = tegra_actmon_account_cpu_freq(tegra, dev, target_freq);
>>  
>> -	return target_freq;
>> +	return min(target_freq, tegra->max_freq);
> 
> Once again, did you meet this case sometimes?

This case happens at least whenever CPU's freq accounting returns
KHZ_MAX, please see actmon_emc_ratios[] and actmon_cpu_to_emc_rate().

> Usually, we can prevent the overflow of target_freq
> when calculating the target frequency or this style.
> 
> I think that if the overflow of target frequency happen frequently,
> it might have the problem of calculation way. 

It is possible to get sampled avg_count from hardware that results in
target_freq > max_freq because translating number of memory events to
memory frequency has some calculation error, although it is negligible.

In fact, it shouldn't matter that the returned target_freq > max_freq
with the current driver's code structure and in the commit's message I
wrote that this change is done for consistency. Hence it should be okay
to drop this patch as well.

  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-11 21:22 [PATCH v6 00/19] More improvements for Tegra30 devfreq driver Dmitry Osipenko
2019-08-11 21:22 ` [PATCH v6 01/19] PM / devfreq: tegra30: Change irq type to unsigned int Dmitry Osipenko
2019-08-11 21:22 ` [PATCH v6 02/19] PM / devfreq: tegra30: Keep interrupt disabled while governor is stopped Dmitry Osipenko
2019-08-20  0:02   ` Chanwoo Choi
2019-08-11 21:22 ` [PATCH v6 03/19] PM / devfreq: tegra30: Handle possible round-rate error Dmitry Osipenko
2019-08-20  0:06   ` Chanwoo Choi
2019-08-11 21:23 ` [PATCH v6 04/19] PM / devfreq: tegra30: Drop write-barrier Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 05/19] PM / devfreq: tegra30: Set up watermarks properly Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 06/19] PM / devfreq: tegra30: Tune up boosting thresholds Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 07/19] PM / devfreq: tegra30: Fix integer overflow on CPU's freq max out Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 08/19] PM / devfreq: tegra30: Ensure that target freq won't overflow Dmitry Osipenko
2019-08-20  0:23   ` Chanwoo Choi
2019-08-20 23:19     ` Dmitry Osipenko [this message]
2019-08-11 21:23 ` [PATCH v6 09/19] PM / devfreq: tegra30: Use kHz units uniformly in the code Dmitry Osipenko
2019-10-01 23:29   ` Chanwoo Choi
2019-10-02 18:26     ` Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 10/19] PM / devfreq: tegra30: Reduce unnecessary interrupts activity Dmitry Osipenko
2019-10-01 23:35   ` Chanwoo Choi
2019-10-02 18:40     ` Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 11/19] PM / devfreq: tegra30: Use CPUFreq notifier Dmitry Osipenko
2019-10-02  0:02   ` Chanwoo Choi
2019-10-02 14:06     ` Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 12/19] PM / devfreq: tegra30: Move clk-notifier's registration to governor's start Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 13/19] PM / devfreq: tegra30: Reset boosting on startup Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 14/19] PM / devfreq: tegra30: Don't enable consecutive-down interrupt " Dmitry Osipenko
2019-10-02  0:04   ` Chanwoo Choi
2019-08-11 21:23 ` [PATCH v6 15/19] PM / devfreq: tegra30: Constify structs Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 16/19] PM / devfreq: tegra30: Include appropriate header Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 17/19] PM / devfreq: tegra30: Increase sampling period to 16ms Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 18/19] PM / devfreq: tegra30: Support variable polling interval Dmitry Osipenko
2019-10-02  0:18   ` Chanwoo Choi
2019-10-02 15:27     ` Dmitry Osipenko
2019-08-11 21:23 ` [PATCH v6 19/19] PM / devfreq: tegra20/30: Add Dmitry as a maintainer Dmitry Osipenko
2019-10-01 21:15 ` [PATCH v6 00/19] More improvements for Tegra30 devfreq driver Dmitry Osipenko
2019-10-02  0:25   ` Chanwoo Choi
2019-10-02 13:54     ` Dmitry Osipenko
2019-10-05 16:29       ` Peter Geis

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