On Tue, Sep 08 2020 at 06:15 -0600, Ulf Hansson wrote:
On Thu, 3 Sep 2020 at 01:26, Lina Iyer <ilina@xxxxxxxxxxxxxx> wrote:
Hello,
I was looking for an option to do better power management for some
domains where the devices enter runtime PM in a predictable fashion. For
example a display device that sends a vsync interrupt every 16 ms for a
60 Hz panel. These interrupts are not timer interrupts but tend to
interrupt periodically to service the workflow and the devices and
domains may go back to idle soon after. Two domains are affected by this
- the device's PM domain and the CPU PM domain.
As a first step, I am looking to solve for the device's PM domain idle
state (and hopefully solve for the CPU PM domains subsequently). The PM
domain could have multiple idle states and/or the enter/exit latencies
could be high. In either case, it may not always be beneficial to power
off the domain, only to turn it back on before satisfying the idle state
residency. When the wakeup is known for the device, we could use that to
determine the worthiness of entering a domain idle state. Only the
device can tell us when the future event would be and that could change
as the usecase changes. Like, when the panel refresh rate increases to
120 Hz. If this information was made available to runtime PM, we could
use that in the domain governor to determine a suitable idle state. This
is the idea behind these patches.
While striving towards entering the most optimal (energy and
performance wise) idle state, I think it's an interesting approach.
Thanks for taking time to review this.
In the first patch, I am proposing an API for devices to specify their
wakeup as a time in the future and in the second patch, I am updating
the PM domain governor to use this information to determine the idle
state. I have not had a chance to test this out yet, but I wanted to
know if I am on the right track.
I don't have any immediate objections - I think the approach seems
reasonable. Still, my first thought that this could be an extension to
the dev_pm_qos interface, but perhaps that isn't a good fit.
Yeah, I did look into that, but it did not the bill exactly either
starting with the locking requirements and how the next event could be
placed from an interrupt context.
I also have a couple of comments to the code, but I will reply to each
patch separately about that.
Would appreciate your thoughts on this.
When it comes to showing real results, other than in theory, I think
Well, the device's PM domain power saving is largely dependent on the
board design and the power saving or performance benefit may not be
easily quantifiable.
we need to make the genpd's cpu governor to cope with the next wakeup
event as well.
I was hoping to tie this with the genirq/timing framework as well for
the CPUs, but it is something I was thinking as a next step. The API and
the governor changes here lay the foundation for that as well. All we
need to do is hook up the predicted event to the CPU device and the CPU
domain governor already calls into the default_power_down_ok() which
takes care of the next event to effect a better governor decision.
--Lina
Thanks,
Lina
Lina Iyer (2):
PM / runtime: register device's next wakeup
PM / Domains: use device's next wakeup to determine domain idle state
drivers/base/power/domain_governor.c | 87 ++++++++++++++++++++++++++--
drivers/base/power/runtime.c | 31 ++++++++++
include/linux/pm.h | 2 +
include/linux/pm_domain.h | 1 +
include/linux/pm_runtime.h | 1 +
5 files changed, 116 insertions(+), 6 deletions(-)
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Kind regards
Uffe
