linux-kernel - Re: [PATCH] PM QoS: Add debugfs support to view the list of constraints

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Date:	Mon, 15 Dec 2014 14:34:15 -0800
From:	Kevin Hilman <khilman@...nel.org>
To:	Dave Gerlach <d-gerlach@...com>
Cc:	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Nishanth Menon <nm@...com>
Subject: Re: [PATCH] PM QoS: Add debugfs support to view the list of constraints

Dave Gerlach <d-gerlach@...com> writes:

> From: Nishanth Menon <nm@...com>
>
> PM QoS requests are notoriously hard to debug and made even
> more so due to their highly dynamic nature. Having visibility
> into the internal data representation per constraint allows
> us to have much better appreciation of potential issues or
> bad usage by drivers in the system.
>
> So introduce for all classes of PM QoS, an entry in
> /sys/kernel/debug/pm_qos that shall show all the current
> requests as well as the snapshot of the value these requests
> boil down to. For example:
> ==> /sys/kernel/debug/pm_qos/cpu_dma_latency <==
> 1: 4444: Active
> 2: 2000000000: Default
> 3: 2000000000: Default
> 4: 2000000000: Default
> Type=Minimum, Value=4444, Requests: active=1 / total=4
>
> ==> /sys/kernel/debug/pm_qos/memory_bandwidth <==
> Empty!
>
> ...
>
> The actual value listed will have their meaning based
> on the QoS it is on, the 'Type' indicates what logic
> it would use to collate the information - Minimum,
> Maximum, or Sum. Value is the collation of all requests.
> This interface also compares the values with the defaults
> for the QoS class and marks the ones that are
> currently active.
>
> Signed-off-by: Nishanth Menon <nm@...com>
> Signed-off-by: Dave Gerlach <d-gerlach@...com>

A very useful feature indeed,

Acked-by: Kevin Hilman <khilman@...aro.org>

Kevin
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