On 2/17/21 12:50 AM, Viresh Kumar wrote:
Hi Thara,
On 16-02-21, 19:00, Thara Gopinath wrote:
This is a fix for a regression observed on db845 platforms with 5.7-rc11
kernel. On these platforms running stress tests with 5.11-rc7 kernel
causes big cpus to overheat and ultimately shutdown the system due to
hitting critical temperature (thermal throttling does not happen and
cur_state of cpufreq cooling device for big cpus remain stuck at 0 or max
frequency).
This platform has boost opp defined for big cpus but boost mode itself is
disabled in the cpufreq driver. Hence the initial max frequency request
from cpufreq cooling device(cur_state) for big cpus is for boost
frequency(2803200) where as initial max frequency request from cpufreq
driver itself is for the highest non boost frequency (2649600).
Okay.
qos
framework collates these two requests and puts the max frequency of big
cpus to 2649600 which the thermal framework is unaware of.
It doesn't need to be aware of that. It sets its max frequency and other
frameworks can put their own requests and the lowest one wins. In this case the
other constraint came from cpufreq-core, which is fine.
Yes. the qos behavior is correct here.
Now during an
over heat event, with step-wise policy governor, thermal framework tries to
throttle the cpu and places a restriction on max frequency of the cpu to
cur_state - 1
Actually it is cur_state + 1 as the values are inversed here, cooling state 0
refers to highest frequency :)
yes. it does indeed!
which in this case 2649600. qos framework in turn tells the
cpufreq cooling device that max frequency of the cpu is already at 2649600
and the cooling device driver returns doing nothing(cur_state of the
cooling device remains unchanged).
And that's where the bug lies, I have sent proper fix for that now.
Like I mention below there are multiple possible fixes for this issue!
More on mismatch of frequencies below.
Thus thermal remains stuck in a loop and
never manages to actually throttle the cpu frequency. This ultimately leads
to system shutdown in case of a thermal overheat event on big cpus.
There are multiple possible fixes for this issue. Fundamentally,it is wrong
for cpufreq driver and cpufreq cooling device driver to show different
maximum possible state/frequency for a cpu.
Not actually, cpufreq core changes the max supported frequency at runtime based
on the availability of boost frequencies.
First of all, I am still unable to find this setting in the sysfs space.
Irrespective the ideal behavior here will be to change the cpufreq
cooling dev max state when this happens. I say this for two reasons
1. The cooling device max state will reflect the correct highest
frequency as reported by cpufreq core. These are interfaces exposed to
user space and they should not be showing two different things.
2. More importantly, thermal will not waste valuable cycles attempting
to throttle down from an non-existing high frequency. In the case of
sdm845 we have only one boost opp in the opp table and hence the first
time thermal tries to throttle via the cpufreq cooling device(with the
step policy governor), it will return back saying that the state is
already achieved and then will retry again because overheating has not
stopped. But let us a platform has 5 such opps in the table and boost
mode not enabled. cpufreq cooling device will have to attempt 5 times
before any actual cooling action happens.
cpufreq_table_count_valid_entries() is used at different places and it is
implemented correctly.
It is used in one other place which is for statistics count. Boost
statistics need not be considered if boost mode is not enabled. And like
I mentioned before as in the case of cpufreq cooling device correct
behavior will be to reflect this as and when boost is enabled. But then
again for statistics purpose it is not much of an issue if the entry
itself is present with the count showing 0 if boost modes are not
enabled. In this case, we should have another api or cpufreq cooling
device not use cpufreq_table_count_valid_entries to get the max state.
--
Warm Regards
Thara
