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

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Message-ID: <4174934.VKXlq5EvTQ@vostro.rjw.lan>
Date:	Fri, 30 Jan 2015 01:10:57 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Kevin Hilman <khilman@...nel.org>
Cc:	Dave Gerlach <d-gerlach@...com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, 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

On Monday, December 15, 2014 02:34:15 PM Kevin Hilman wrote:
> 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>

Queued up for 3.20, thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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