linux-kernel - Re: [PATCH] PM / QoS: Fix device resume latency PM QoS

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Date:   Mon, 23 Oct 2017 13:12:43 +0800
From:   Alex Shi <alex.shi@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Ramesh Thomas <ramesh.thomas@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH] PM / QoS: Fix device resume latency PM QoS



On 10/20/2017 07:27 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The special value of 0 for device resume latency PM QoS means
> "no restriction", but there are two problems with that.
> 
> First, device resume latency PM QoS requests with 0 as the
> value are always put in front of requests with positive
> values in the priority lists used internally by the PM QoS
> framework, causing 0 to be chosen as an effective constraint
> value.  However, that 0 is then interpreted as "no restriction"
> effectively overriding the other requests with specific
> restrictions which is incorrect.
> 
> Second, the users of device resume latency PM QoS have no
> way to specify that *any* resume latency at all should be
> avoided, which is an artificial limitation in general.
> 
> To address these issues, modify device resume latency PM QoS to
> use S32_MAX as the "no constraint" value and 0 as the "no
> latency at all" one and rework its users (the cpuidle menu
> governor, the genpd QoS governor and the runtime PM framework)
> to follow these changes.
> 
> Also add a special "n/a" value to the corresponding user space I/F
> to allow user space to indicate that it cannot accept any resume
> latencies at all for the given device.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Reported-by: Reinette Chatre <reinette.chatre@...el.com>


Acked-by: Alex Shi <alex.shi@...aro.org>