linux-kernel - Re: [PATCH 07/11] PM / devfreq: check get_dev

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Message-ID: <CAA+hA=T3A=FW-kCu=3jDTP+o3JpPYVB6VnphazXVkybGZCanaQ@mail.gmail.com>
Date:   Sat, 13 Mar 2021 14:45:39 +0800
From:   Dong Aisheng <dongas86@...il.com>
To:     Chanwoo Choi <cwchoi00@...il.com>
Cc:     Chanwoo Choi <cw00.choi@...sung.com>,
        Dong Aisheng <aisheng.dong@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        dl-linux-imx <linux-imx@....com>,
        open list <linux-kernel@...r.kernel.org>,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        Abel Vesa <abel.vesa@....com>
Subject: Re: [PATCH 07/11] PM / devfreq: check get_dev_status before start monitor

On Sat, Mar 13, 2021 at 12:09 AM Chanwoo Choi <cwchoi00@...il.com> wrote:
>
> On 21. 3. 12. 오후 7:57, Dong Aisheng wrote:
> > On Thu, Mar 11, 2021 at 2:54 PM Chanwoo Choi <cw00.choi@...sung.com> wrote:
> >>
> >> On 3/10/21 1:56 PM, Dong Aisheng wrote:
> >>> On Wed, Mar 10, 2021 at 11:08 AM Chanwoo Choi <cw00.choi@...sung.com> wrote:
> >>>>
> >>>> On 3/10/21 11:56 AM, Dong Aisheng wrote:
> >>>>> On Wed, Mar 10, 2021 at 12:12 AM Chanwoo Choi <cwchoi00@...il.com> wrote:
> >>>>>>
> >>>>>> On 21. 3. 10. 오전 12:58, Chanwoo Choi wrote:
> >>>>>>> On 21. 3. 9. 오후 9:58, Dong Aisheng wrote:
> >>>>>>>> The devfreq monitor depends on the device to provide load information
> >>>>>>>> by .get_dev_status() to calculate the next target freq.
> >>>>>>>>
> >>>>>>>> And this will cause changing governor to simple ondemand fail
> >>>>>>>> if device can't support.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> >>>>>>>> ---
> >>>>>>>>    drivers/devfreq/devfreq.c                 | 10 +++++++---
> >>>>>>>>    drivers/devfreq/governor.h                |  2 +-
> >>>>>>>>    drivers/devfreq/governor_simpleondemand.c |  3 +--
> >>>>>>>>    3 files changed, 9 insertions(+), 6 deletions(-)
> >>>>>>>>
> >>>>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> >>>>>>>> index 7231fe6862a2..d1787b6c7d7c 100644
> >>>>>>>> --- a/drivers/devfreq/devfreq.c
> >>>>>>>> +++ b/drivers/devfreq/devfreq.c
> >>>>>>>> @@ -482,10 +482,13 @@ static void devfreq_monitor(struct work_struct
> >>>>>>>> *work)
> >>>>>>>>     * to be called from governor in response to DEVFREQ_GOV_START
> >>>>>>>>     * event when device is added to devfreq framework.
> >>>>>>>>     */
> >>>>>>>> -void devfreq_monitor_start(struct devfreq *devfreq)
> >>>>>>>> +int devfreq_monitor_start(struct devfreq *devfreq)
> >>>>>>>>    {
> >>>>>>>>        if (IS_SUPPORTED_FLAG(devfreq->governor->flags, IRQ_DRIVEN))
> >>>>>>>> -        return;
> >>>>>>>> +        return 0;
> >>>>>>>> +
> >>>>>>>> +    if (!devfreq->profile->get_dev_status)
> >>>>>>>> +        return -EINVAL;
> >>>>>>
> >>>>>> Again, I think that get_dev_status is not used for all governors.
> >>>>>> So that it cause the governor start fail. Don't check whether
> >>>>>> .get_dev_status is NULL or not.
> >>>>>>
> >>>>>
> >>>>> I'm not quite understand your point.
> >>>>> it is used by governor_simpleondemand.c and tegra_devfreq_governor.
> >>>>> get_target_freq -> devfreq_update_stats -> get_dev_status
> >>>>
> >>>> The devfreq can add the new governor by anyone.
> >>>> So these functions like devfreq_monitor_* have to support
> >>>> the governors and also must support the governor to be added
> >>>> in the future.
> >>>
> >>> Yes, but devfreq_monitor_* is only used by polling mode, right?
> >>> The governor using it has to implement get_dev_status unless
> >>> there's an exception in the future.
> >>>
> >>> Currently this patch wants to address the issue that user can switch
> >>> to ondemand governor (polling mode) by sysfs even devices does
> >>> not support it (no get_dev_status implemented).
> >>
> >> As I commented, I'll fix this issue. If devfreq driver doesn't implement
> >> the .get_dev_status, don't show it via available_governors. I think that
> >> it is fundamental solution to fix this issue.
> >
> > Sounds good
> >
> >> So on this version,
> >> don't add the this conditional statement on this function
> >>
> >
> > Almost all this patch did is adding a checking for get_dev_status.
> > So do you mean drop this patch?
> > I wonder it's still a necessary checking to explicitly tell devfreq monitor
> > users that get_dev_status is needed during governor startup.
>
> I think that the it is enough to check .get_dev_status in
> devfreq_update_stats. We have to check it on where it is used.
>

I think the drawback of only checking .get_dev_status in
devfreq_update_stats is:
1. devfreq will still register successfully and ondemand governor starts ok
2. ondemand governor will still be shown in sysfs which is something
you want to fix
3. devfreq will end up printing endless error messages in devfreq_monitor worker
    "dvfs failed with (%d) error" as the possible missing .get_dev_status

So i wonder if you don't like changing the common devfreq_monitor_start in order
to make it look common for all governors, then we probably still need
to fix it in
ondemand governor in order to avoid the possible above issues.

static int devfreq_simple_ondemand_handler(struct devfreq *devfreq,
                                unsigned int event, void *data)
{
        switch (event) {
        case DEVFREQ_GOV_START:
                if (!devfreq->profile->get_dev_status)
                        return -EINVAL;

                return devfreq_monitor_start(devfreq);
...
}

How do you think?

Regards
Aisheng


> >
> >> And on next version, please use the capital letter for first character
> >> on patch title as following:
> >>
> >> - PM / devfreq: Check get_dev_status before start monitor
> >>
> >
> > Okay to me.
> > Thanks for the suggestion.
> >
> > Regards
> > Aisheng
> >
> >>>
> >>> Regards
> >>> Aisheng
> >>>
> >>>>
> >>>>>
> >>>>> Without checking, device can switch to ondemand governor if it does not support.
> >>>>>
> >>>>> Am i missed something?
> >>>>>
> >>>>> Regards
> >>>>> Aisheng
> >>>>>
> >>>>>>>>        switch (devfreq->profile->timer) {
> >>>>>>>>        case DEVFREQ_TIMER_DEFERRABLE:
> >>>>>>>> @@ -495,12 +498,13 @@ void devfreq_monitor_start(struct devfreq *devfreq)
> >>>>>>>>            INIT_DELAYED_WORK(&devfreq->work, devfreq_monitor);
> >>>>>>>>            break;
> >>>>>>>>        default:
> >>>>>>>> -        return;
> >>>>>>>> +        return -EINVAL;
> >>>>>>>>        }
> >>>>>>>>        if (devfreq->profile->polling_ms)
> >>>>>>>>            queue_delayed_work(devfreq_wq, &devfreq->work,
> >>>>>>>>                msecs_to_jiffies(devfreq->profile->polling_ms));
> >>>>>>>> +    return 0;
> >>>>>>>>    }
> >>>>>>>>    EXPORT_SYMBOL(devfreq_monitor_start);
> >>>>>>>> diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
> >>>>>>>> index 5cee3f64fe2b..31af6d072a10 100644
> >>>>>>>> --- a/drivers/devfreq/governor.h
> >>>>>>>> +++ b/drivers/devfreq/governor.h
> >>>>>>>> @@ -75,7 +75,7 @@ struct devfreq_governor {
> >>>>>>>>                    unsigned int event, void *data);
> >>>>>>>>    };
> >>>>>>>> -void devfreq_monitor_start(struct devfreq *devfreq);
> >>>>>>>> +int devfreq_monitor_start(struct devfreq *devfreq);
> >>>>>>>>    void devfreq_monitor_stop(struct devfreq *devfreq);
> >>>>>>>>    void devfreq_monitor_suspend(struct devfreq *devfreq);
> >>>>>>>>    void devfreq_monitor_resume(struct devfreq *devfreq);
> >>>>>>>> diff --git a/drivers/devfreq/governor_simpleondemand.c
> >>>>>>>> b/drivers/devfreq/governor_simpleondemand.c
> >>>>>>>> index d57b82a2b570..ea287b57cbf3 100644
> >>>>>>>> --- a/drivers/devfreq/governor_simpleondemand.c
> >>>>>>>> +++ b/drivers/devfreq/governor_simpleondemand.c
> >>>>>>>> @@ -89,8 +89,7 @@ static int devfreq_simple_ondemand_handler(struct
> >>>>>>>> devfreq *devfreq,
> >>>>>>>>    {
> >>>>>>>>        switch (event) {
> >>>>>>>>        case DEVFREQ_GOV_START:
> >>>>>>>> -        devfreq_monitor_start(devfreq);
> >>>>>>>> -        break;
> >>>>>>>> +        return devfreq_monitor_start(devfreq);
> >>>>>>>>        case DEVFREQ_GOV_STOP:
> >>>>>>>>            devfreq_monitor_stop(devfreq);
> >>>>>>>>
> >>>>>>>
> >>>>>>> Need to handle the all points of devfreq_monitor_start() usage.
> >>>>>>> please check the tegra30-devfreq.c for this update.
> >>>>>>>
> >>>>>>> $ grep -rn "devfreq_monitor_start" drivers/
> >>>>>>> drivers/devfreq/governor_simpleondemand.c:92:
> >>>>>>> devfreq_monitor_start(devfreq);
> >>>>>>> drivers/devfreq/tegra30-devfreq.c:744:
> >>>>>>> devfreq_monitor_start(devfreq);
> >>>>>>> ......
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>>> --
> >>>>>> Best Regards,
> >>>>>> Samsung Electronics
> >>>>>> Chanwoo Choi
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>> --
> >>>> Best Regards,
> >>>> Chanwoo Choi
> >>>> Samsung Electronics
> >>>
> >>>
> >>
> >>
> >> --
> >> Best Regards,
> >> Chanwoo Choi
> >> Samsung Electronics
>
>
> --
> Best Regards,
> Samsung Electronics
> Chanwoo Choi