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

[Lionel Landwerlin]

On 12/03/2020 21:27, Dixit, Ashutosh wrote:
> 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


Sure, just make sure the users know about this.

The fact that they can now select timer values that will potentially 
lead to the loss of the buffer's data because it was overridden.


Thanks,

-Lionel