On 2018-08-01 09:03, Sudeep Holla wrote:
On 28/07/18 04:56, Saravana Kannan wrote:
Many CPU architectures have caches that can scale independent of the
CPUs.
Frequency scaling of the caches is necessary to make sure the cache is
not
a performance bottleneck that leads to poor performance and power. The
same
idea applies for RAM/DDR.
To achieve this, this patch adds a generic devfreq governor that can
listen
to the frequency transitions of each CPU frequency domain and then
adjusts
the frequency of the cache (or any devfreq device) based on the
frequency
of the CPUs.
To decide the frequency of the device, the governor does one of the
following:
* Uses a CPU frequency to device frequency mapping table
- Either one mapping table used for all CPU freq policies (typically
used
for system with homogeneous cores/clusters that have the same
OPPs.
- One mapping table per CPU freq policy (typically used for ASMP
systems
with heterogeneous CPUs with different OPPs)
OR
* Scales the device frequency in proportion to the CPU frequency. So,
if
the CPUs are running at their max frequency, the device runs at its
max
frequency. If the CPUs are running at their min frequency, the
device
runs at its min frequency. And interpolated for frequencies in
between.
Is this solution for the old generation of SDM ?
This code isn't even specific to Qualcomm chips. Let alone a specific
generation of SDM.
I have seen newer ones have some kind of firmware interface/hardware to
deal with CPUFreq. Do you need this solution for them too ?
You are confusing two completely unrelated drivers. This is generic
*devfreq* *governor* code. I'll be renaming the commit text like Rafael
suggested.
Something like: CPU frequency to devfreq mapping governor.
If yes, why ?
Read the commit text.
IMO firmware can arbitrate various requests for frequency
scaling and do the *right thing* for the platform.
Firmware (if any) can arbitrate HW that it controls. DDR and
interconnect is not something a firmware might control (or should
control).
Having OSPM sending
separate requests for such bus/interconnect might end up with
conflicts.
No ?
If some chips have firmware that takes care of everything, then you
obviously won't be enabling any power management code.
Thanks,
Saravana
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