[Intel-gfx] [PATCH 4/7] drm/i915/perf: add new open param to configure polling of OA buffer

[Dixit, Ashutosh]

On Tue, 03 Mar 2020 14:19:02 -0800, Umesh Nerlige Ramappa wrote:
>
> From: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
>
> This new parameter let's the application choose how often the OA
> buffer should be checked on the CPU side for data availability. Longer
> polling period tend to reduce CPU overhead if the application does not
> care about somewhat real time data collection.
>
> v2: Allow disabling polling completely with 0 value (Lionel)
> v3: Version the new parameter (Joonas)
> v4: Rebase (Umesh)

Hi Lionel, I was thinking that one way to keep things simple for now (and
fix the high cpu usage issue) would be to expose _ONLY_ this OA poll period
parameter to user space. That is we don't expose the interrupt or the flush
ioctl to user space at this time. This way the user will be able to
configure the hrtimer frequency to a lower value to bring down the cpu
usage.

Also we would disallow disabling the timer (and internally also not use the
interrupt). So everything will happen in exactly the same way as it used to
(no other changes needed) but at a lower rate if the user so chooses.

What do you think about this?

Thanks!
--
Ashutosh