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

[Umesh Nerlige Ramappa]

On Thu, Mar 12, 2020 at 10:37:12PM +0200, Lionel Landwerlin wrote:
>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.
>

posted v2:
Kernel patches - https://patchwork.freedesktop.org/series/54280/#rev6
IGT - https://patchwork.freedesktop.org/series/74655/

Thanks,
Umesh

>
>Thanks,
>
>-Lionel
>