Hi Daniel,
On 12/7/20 12:41 PM, Lukasz Luba wrote:
On 12/3/20 4:09 PM, Daniel Lezcano wrote:
On 03/12/2020 16:38, Lukasz Luba wrote:
On 12/3/20 1:09 PM, Daniel Lezcano wrote:
On 18/11/2020 13:03, Lukasz Luba wrote:
Devfreq cooling needs to now the correct status of the device in order
to operate. Do not rely on Devfreq last_status which might be a stale
data
and get more up-to-date values of the load.
Devfreq framework can change the device status in the background. To
mitigate this situation make a copy of the status structure and use it
for internal calculations.
In addition this patch adds normalization function, which also makes
sure
that whatever data comes from the device, it is in a sane range.
Signed-off-by: Lukasz Luba <lukasz.luba@xxxxxxx>
---
drivers/thermal/devfreq_cooling.c | 52
+++++++++++++++++++++++++------
1 file changed, 43 insertions(+), 9 deletions(-)
diff --git a/drivers/thermal/devfreq_cooling.c
b/drivers/thermal/devfreq_cooling.c
index 659c0143c9f0..925523694462 100644
--- a/drivers/thermal/devfreq_cooling.c
+++ b/drivers/thermal/devfreq_cooling.c
@@ -227,20 +227,46 @@ static inline unsigned long
get_total_power(struct devfreq_cooling_device *dfc,
voltage);
}
+static void _normalize_load(struct devfreq_dev_status *status)
+{
+ /* Make some space if needed */
+ if (status->busy_time > 0xffff) {
+ status->busy_time >>= 10;
+ status->total_time >>= 10;
+ }
+
+ if (status->busy_time > status->total_time)
+ status->busy_time = status->total_time;
How the condition above is possible?
They should, be checked by the driver, but I cannot trust
and have to check for all corner cases: (div by 0, overflow
one of them, etc). The busy_time and total_time are unsigned long,
which means 4B on 32bit machines.
If these values are coming from device counters, which count every
busy cycle and total cycles of a clock of a device running at e.g.
1GHz they would overflow every ~4s.
I don't think it is up to this routine to check the driver is correctly
implemented, especially at every call to get_requested_power.
If the normalization ends up by doing this kind of thing, there is
certainly something wrong in the 'status' computation to be fixed before
submitting this series.
Normally IPA polling are 1s and 100ms, it's platform specific. But there
are also 'empty' periods when IPA sees temperature very low and does not
even call the .get_requested_power() callbacks for the cooling devices,
just grants max freq to all. This is problematic. I am investigating it
and will propose a solution for IPA soon.
I would avoid all of this if devfreq core would have default for all
devices a reliable polling timer... Let me check some possibilities also
for this case.
Ok, may be create an API to compute the 'idle,busy,total times' to be
used by the different the devfreq drivers and then fix the overflow in
this common place.
Yes, I have this plan, but I have to close this patch series. To go
forward with this, I will drop the normalization function and will keep
only the code of safe copy of the 'status', so using busy_time and
total_time will be safe.
I did experiments and actually I cannot drop this function. Drivers can
feed total_time and busy_time which are in nanoseconds, e.g. [1] 50ms =>
50.000.000ns which is then when multiplied by 1024 and exceed the u32.
I want to avoid 64bit variables and divisions, so shifting them earlier
would help. IMHO it does not harm this devfreq cooling to make that
check and handle ns values.
I am going to use the normalization into 0..1024 as you and Ionela
suggested.
I will also drop the direct device status check. That would be a
different patch series. In that patch set I will try to come with a
generic solution and some API.
Regards,
Lukasz
[1]
https://elixir.bootlin.com/linux/v5.10-rc5/source/drivers/gpu/drm/panfrost/panfrost_devfreq.c#L66
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