Re: [linux-pm] [RFC/PATCH 0/9] PM QoS: add a per-device wake-up latency constraint class

From: mark gross <markgross@thegnar.org>
To: jean.pihet@newoldbits.com
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Paul Walmsley <paul@pwsan.com>,
	Kevin Hilman <khilman@ti.com>,
	Magnus Damm <magnus.damm@gmail.com>,
	Linux PM mailing list <linux-pm@lists.linux-foundation.org>,
	linux-omap@vger.kernel.org, Jean Pihet <j-pihet@ti.com>
Subject: Re: [linux-pm] [RFC/PATCH 0/9] PM QoS: add a per-device wake-up latency constraint class
Date: Mon, 27 Jun 2011 06:40:19 -0700	[thread overview]
Message-ID: <20110627134019.GA14826@gvim.org> (raw)
In-Reply-To: <1308926286-30445-1-git-send-email-j-pihet@ti.com>

On Fri, Jun 24, 2011 at 04:37:57PM +0200, jean.pihet@newoldbits.com wrote:
> From: Jean Pihet <j-pihet@ti.com>
> 
> This patch set is in an RFC state, for review and comments.
> 
> In order to implement the new class in PM QoS the following changes
> have been made:
> 
> 1. Add a new PM QoS class for device wake-up constraints
> (PM_QOS_DEV_WAKEUP_LATENCY).  Due to the per-device nature of the new
> class the constraints lists are stored inside the device dev_pm_info
> struct instead of the internal per-class constraints lists.  The new
> class is only available from kernel drivers and so is not exported to
> user space.

I have not looked at the patch yet but, this reads like "add a
constraint class per LDM device in the current os"  I assume it would
add and destroy them with driver load / unloads.  I wonder how that
would work in practice.  Probubly need an notifier or a silent failure
for constraint dependents  with stale refs to the device.

Historically, I had initially implemented pm_qos to support dynamic
creation of constraint classes.  But, the feedback I got on that was
that "we can't trust driver writers" so lets not enable that.  Perhaps
keeping such constraints not exposed to user mode gets around the
objection we had back then.

> 
> 2. Make the pm_qos_add_request API more generic by using a struct
> pm_qos_parameters parameter. This allows easy extension in the future.
> 
> 3. Upon a change of the strongest constraint in the
> PM_QOS_DEV_WAKEUP_LATENCY class a notification chain mechanism is used

strongest constraint?  Do you mean the aggregated constraint?

> to take action on the system. This is the proposed way to have PM QoS
> and the platform dependant code to interact with each other, cf. 4
> below.  The notification mechanism now passes the constraint request
> struct ptr in order for the notifier callback to have access to the
> full set of constraint data, e.g. the struct device ptr.
> 
> 4. cpuidle interaction with the OMAP3 cpuidle handler
> Since cpuidle is a CPU centric framework it decides the MPU next power
> state based on the MPU exit_latency and target_residency figures.
>     
> The rest of the power domains get their next power state programmed
> from the PM_QOS_DEV_WAKEUP_LATENCY class of the PM QoS framework, via
> the device wake-up latency constraints.
> 
> Note: the exit_latency and target_residency figures of the MPU include
> the MPU itself and the peripherals needed for the MPU to execute
> instructions (e.g. main memory, caches, IRQ controller, MMU etc).
> Some of those peripherals can belong to other power domains than the
> MPU subsystem and so the corresponding latencies must be included in
> this figure.
> 
> 5. Update the pm_qos_add_request callers to the generic API
> 
> 6. Minor clean-ups and rename of struct fields
> 
> Questions:
> 1. How to retrieve the device ptr from a given device driver in order
> to add a constraint on it?
put the pm_qos constraint class data into the LDM so all devices
implicitly have a constraint class associated with each is my first
thought.  Of course you still have the problem of one driver getting the
handle to the constraint class of some other driver.  hmmm that is a
messy problem.

Might not be a popular idea...

I'll look at the patch details and have more thoughts on this soon.

--mark
> 2. The device struct has been extended with the power domain
> information. Can this be used to apply the constraints on power
> domains, as proposed by [1]?
> 
> On-going developments, patches in preparation:
> 1. write Documentation for the new PM QoS class
> 2. validate the constraints framework on OMAP3&4
> 3. refine the power domains wake-up latency and the cpuidle figures
> 
> [1] http://marc.info/?l=linux-omap&m=130451613408148&w=2
> 
> Based on the master branch of the linux-omap git tree (3.0.0-rc3). Compile tested only using OMAP and x86 generic defconfigs.
> 
> 
> Jean Pihet (8):
>   PM: add a per-device wake-up latency constraints plist
>   PM: extend PM QoS with per-device wake-up constraints
>   OMAP PM: create a PM layer plugin for per-device constraints
>   OMAP2+: powerdomain: control power domains next state
>   OMAP3: powerdomain data: add wake-up latency figures
>   OMAP2+: omap_hwmod: manage the wake-up latency constraints
>   OMAP: PM CONSTRAINTS: implement the devices wake-up latency
>     constraints
>   OMAP2+: cpuidle only influences the MPU state
> 
> Vishwanath BS (1):
>   OMAP4: powerdomain data: add wake-up latency figures
> 
>  arch/arm/mach-omap2/cpuidle34xx.c            |   42 +---
>  arch/arm/mach-omap2/omap_hwmod.c             |   26 ++-
>  arch/arm/mach-omap2/pm.h                     |   17 ++-
>  arch/arm/mach-omap2/powerdomain.c            |  187 ++++++++++++++
>  arch/arm/mach-omap2/powerdomain.h            |   33 +++-
>  arch/arm/mach-omap2/powerdomains3xxx_data.c  |   77 ++++++
>  arch/arm/mach-omap2/powerdomains44xx_data.c  |   85 +++++++
>  arch/arm/plat-omap/Kconfig                   |    7 +
>  arch/arm/plat-omap/Makefile                  |    1 +
>  arch/arm/plat-omap/i2c.c                     |   20 --
>  arch/arm/plat-omap/include/plat/omap-pm.h    |  128 ----------
>  arch/arm/plat-omap/include/plat/omap_hwmod.h |    2 +
>  arch/arm/plat-omap/omap-pm-constraints.c     |  344 ++++++++++++++++++++++++++
>  arch/arm/plat-omap/omap-pm-noop.c            |   89 -------
>  drivers/base/power/main.c                    |    1 +
>  drivers/i2c/busses/i2c-omap.c                |   35 ++-
>  drivers/media/video/via-camera.c             |    5 +-
>  drivers/net/e1000e/netdev.c                  |    9 +-
>  drivers/net/wireless/ipw2x00/ipw2100.c       |    6 +-
>  include/linux/pm.h                           |    2 +
>  include/linux/pm_qos_params.h                |   40 ++--
>  kernel/pm_qos_params.c                       |  142 ++++++-----
>  sound/core/pcm_native.c                      |    8 +-
>  23 files changed, 939 insertions(+), 367 deletions(-)
>  create mode 100644 arch/arm/plat-omap/omap-pm-constraints.c
> 
> -- 
> 1.7.4.1
> 
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