On 01/04/2021 11:24, Tamminen, Eero T wrote:
Hi,
On Thu, 2021-04-01 at 05:54 -0400, Rodrigo Vivi wrote:
On Thu, Apr 01, 2021 at 10:38:11AM +0100, Tvrtko Ursulin wrote:
...
I think it is possible to argue both ways.
1)
HAS_RC6 means hardware has RC6 so if we view PMU as very low level
we can
say always export it.
If i915 had to turn it off (rc6->supported == false) due firmware or
GVT-g,
then we could say reporting zero RC6 is accurate in that sense. Only
the
reason "why it is zero" is missing for PMU users.
2)
Or if we go with this patch we could say that presence of the PMU
metric
means RC6 is active and enabled, while absence means it is either
not
supported due platform (or firmware) or how the platform is getting
used
(GVT-g).
yeap, these 2 cases described well my mental conflict...
So I think patch is a bit better. I don't see it is adding more
confusion.
As I said on the other patch I have no strong position on which is
better,
but if you and Eero feel that this works better for the current case,
let's do it...
IMHO seeing case 1) i.e. zero RC6 could be slightly better from user
point of view than not seeing RC6 at all, because:
A) user then knows that GPU is not entering RC6, and
B) then the question is why it's not going to RC6 => one can see from
sysfs that it has been disabled
Whereas in case 2), the question is why there's no RC6 info, and user
doesn't know whether GPU is suspended or not (i.e. why GPU power
consumption is higher than expected). It would help if i-g-t could show
e.g. "RC6 OFF" in that case.
So many options.. :)
It can be handle on the "presentation" layer (intel_gpu_top). If we go
with this patch but different errnos it could indeed distinguish and
either not show RC6 or say "RC6 OFF".
If we go with the other patch
(https://patchwork.freedesktop.org/patch/426589/?series=88580&rev=1)
then intel_gpu_top could really still do the same by looking at
/sys/class/drm/card0/power/rc6_enable.
So strictly no i915 patch is even needed to provide clarity in
intel_gpu_top.
But still one of those two i915 patches is required to improve how
low-level Perf/PMU RC6 counter gets exposed (or not exposed). I don't
have a strong preference which one to take either. :)
Regards,
Tvrtko
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