Re: [PATCH 00/17] Add OA functionality to Xe

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Tue, 21 May 2024 07:47:58 -0700, Souza, Jose wrote:

Hi Jose,

> > Other ask, can you remove this 'Failed to remove unknown OA config'
> > debug message from xe_oa_remove_config_ioctl()?
>
> Missed 'Insufficient privileges to remove xe OA config', that need to be
> removed too from xe_oa_remove_config_ioctl().
>
> > Mesa will be using DRM_XE_PERF_OP_REMOVE_CONFIG with config id set to
> > UINT64_MAX to detect if Xe KMD supports OA counters and if application
> > has enough permissions to use it.  So it causes dmesg to be flooded
> > with 'xe 0000:00:02.0: [drm:xe_oa_remove_config_ioctl [xe]] Failed to
> > remove unknown OA config' messages when running tests suites.
> >
> > Or do you have other suggestion of uAPI that I can use.

OK, so you are relying on ENODEV and EACCES errno's from
DRM_XE_PERF_OP_REMOVE_CONFIG to find out (a) if OA is present and (b) if
you need to be root (actually CAP_PERFMON or CAP_SYS_ADMIN).

This logic in Xe should be close to what we have in i915? What does Mesa do
for i915, or what doesn't work in Xe?

Here are some pointers:

* You can execute DRM_XE_DEVICE_QUERY_OA_UNITS to see if OA is present

* Add/remove OA configs and using the global OAG buffer (time based
  sampling or DRM_XE_OA_PROPERTY_SAMPLE_OA set) are priviliged operations
  (need root). Operations which only need OAR/OAC (OA queries, without
  DRM_XE_OA_PROPERTY_SAMPLE_OA) can be executed by non-root.

* If "/proc/sys/dev/xe/perf_stream_paranoid" is 0, all operations can be
  executed by non-root users. Otherwise, as I described in the previous
  point.

So basically I think you just need to check for the perf_stream_paranoid
file above. It will tell you both (a) if OA is present (because we are
going to merge the code which creates this file together with OA) and (b)
if you need to be root for particular operations.

Thanks.
--
Ashutosh