[Intel-gfx] [PATCH v7 10/12] drm/i915/perf: allow holding preemption on filtered ctx

[Lionel Landwerlin]

On 09/07/2019 13:00, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2019-07-09 10:32:06)
>> We would like to make use of perf in Vulkan. The Vulkan API is much
>> lower level than OpenGL, with applications directly exposed to the
>> concept of command buffers (pretty much equivalent to our batch
>> buffers). In Vulkan, queries are always limited in scope to a command
>> buffer. In OpenGL, the lack of command buffer concept meant that
>> queries' duration could span multiple command buffers.
>>
>> With that restriction gone in Vulkan, we would like to simplify
>> measuring performance just by measuring the deltas between the counter
>> snapshots written by 2 MI_RECORD_PERF_COUNT commands, rather than the
>> more complex scheme we currently have in the GL driver, using 2
>> MI_RECORD_PERF_COUNT commands and doing some post processing on the
>> stream of OA reports, coming from the global OA buffer, to remove any
>> unrelated deltas in between the 2 MI_RECORD_PERF_COUNT.
>>
>> Disabling preemption only apply to a single context with which want to
>> query performance counters for and is considered a privileged
>> operation, by default protected by CAP_SYS_ADMIN. It is possible to
>> enable it for a normal user by disabling the paranoid stream setting.
>>
>> v2: Store preemption setting in intel_context (Chris)
>>
>> v3: Use priorities to avoid preemption rather than the HW mechanism
>>
>> v4: Just modify the port priority reporting function
>>
>> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
>> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> Could you split this into two -- separate the backend mechanism from
> perf setting the flag? I want to add a selftest and apply.
> -Chris
>
Sure.


-Lionel