linux-kernel - Re: [RFC PATCH 1/4] PM / QoS: Add pm_qos_cancel_request

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Date:	Tue, 21 Apr 2015 13:25:45 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Dov Levenglick <dovl@...eaurora.org>
CC:	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Kevin Hilman <khilman@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/4] PM / QoS: Add pm_qos_cancel_request_lazy() that
 doesn't sleep

On 21/04/15 13:18, Dov Levenglick wrote:
>> On 20/04/15 17:00, Dov Levenglick wrote:
>>>> Add pm_qos_cancel_request_lazy() which is convenient for
>>>> contexts that may not sleep.
>>>>
>>>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>>>> ---
>>>>  include/linux/pm_qos.h |  2 ++
>>>>  kernel/power/qos.c     | 20 ++++++++++++++++++++
>>>>  2 files changed, 22 insertions(+)
>>>>
>>>> diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
>>>> index 7b3ae0c..f44d353 100644
>>>> --- a/include/linux/pm_qos.h
>>>> +++ b/include/linux/pm_qos.h
>>>> @@ -126,6 +126,8 @@ void pm_qos_update_request(struct pm_qos_request
>> *req,
>>>>  			   s32 new_value);
>>>>  void pm_qos_update_request_timeout(struct pm_qos_request *req,
>>>>  				   s32 new_value, unsigned long
>>>> timeout_us);
>>>> +void pm_qos_cancel_request_lazy(struct pm_qos_request *req,
>>>> +				unsigned int timeout_us);
>>>>  void pm_qos_remove_request(struct pm_qos_request *req);
>>>>
>>>
>>> I think that this could be acheived using existing API if
>>> pm_qos_update_request_timeout() were to be called with the existing
>>> timeout value.
>>
>> I don't follow what you mean. There is no existing timeout value.
>> Did you mean existing request value? There is still the difference wrt
>> cancel_delayed_work_sync.
> 
> I did mean the existing request value. Thanks.
> There is also the cancel_delayed_work_sync, however I think that that
> should be called in any case in order to cancel any other pending timeout
> changes.

That might sleep which defeats one of the reasons for creating
pm_qos_cancel_request_lazy().

> 
>>
>>> Since reading the existing timeout value is missing - and I think would
>> be
>>> a useful feature to have for other use-cases - do you agree with such an
>>> approach?
>>>
>>>>  int pm_qos_request(int pm_qos_class);
>>>> diff --git a/kernel/power/qos.c b/kernel/power/qos.c
>>>> index 97b0df7..ac131cb 100644
>>>> --- a/kernel/power/qos.c
>>>> +++ b/kernel/power/qos.c
>>>> @@ -517,6 +517,26 @@ void pm_qos_update_request_timeout(struct
>>>> pm_qos_request *req, s32 new_value,
>>>>  }
>>>>
>>>>  /**
>>>> + * pm_qos_cancel_request_lazy - cancels an existing qos request
>> lazily.
>>>> + * @req : handle to list element holding a pm_qos request to use
>>>> + * @timeout_us: the delay before cancelling this qos request in usecs.
>>>> + *
>>>> + * After timeout_us, this qos request is cancelled.
>>>> + */
>>>> +void pm_qos_cancel_request_lazy(struct pm_qos_request *req,
>>>> +				unsigned int timeout_us)
>>>> +{
>>>> +	if (!req)
>>>> +		return;
>>>> +	if (WARN(!pm_qos_request_active(req),
>>>> +		 "%s called for unknown object.", __func__))
>>>> +		return;
>>>> +
>>>> +	schedule_delayed_work(&req->work, usecs_to_jiffies(timeout_us));
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(pm_qos_cancel_request_lazy);
>>>> +
>>>> +/**
>>>>   * pm_qos_remove_request - modifies an existing qos request
>>>>   * @req: handle to request list element
>>>>   *
>>>> --
>>>> 1.9.1
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-mmc" in
>>>> the body of a message to majordomo@...r.kernel.org
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>>>>
>>>
>>>
>>> QUALCOMM ISRAEL, on behalf of Qualcomm Innovation Center, Inc.
>>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
>> Forum,
>>> a Linux Foundation Collaborative Project
>>>
>>>
>>>
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-mmc" in
>> the body of a message to majordomo@...r.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 
> 
> QUALCOMM ISRAEL, on behalf of Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 
> 
> 

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