[Mesa-dev] [PATCH 2/2] i965: Add support for GL_AMD_performance_monitor on Ironlake.

[Kenneth Graunke]

On 04/12/2013 11:21 AM, Eric Anholt wrote:
> Kenneth Graunke <kenneth at whitecape.org> writes:
>
>> Ironlake's counters are always enabled; userspace can simply send a
>> MI_REPROT_PERF_COUNT packet to take a snapshot of them.  This makes it
>> easy to implement.
>>
>> The counters are documented in the source code for the intel-gpu-tools
>> intel_perf_counters utility.
>
>> +/**
>> + * i965 representation of a performance monitor object.
>> + */
>> +struct brw_perf_monitor_object
>> +{
>> +   /** The base class. */
>> +   struct gl_perf_monitor_object base;
>> +
>> +   /**
>> +    * The GPU-facing BO, holding raw counter data in a hardware specific form.
>> +    */
>> +   drm_intel_bo *gpu_facing_bo;
>> +};
>
> Why all the emphasis of "GPU-facing"?  We don't use BOs for anything
> that the GPU doesn't touch.

At one point, I thought that we returned the data to the application in 
a buffer object...so we'd have two BOs, one GPU-facing, and one 
API-facing.  But we actually just copy it to them via a normal pointer, 
so the careful distinction isn't necessary.

I'll rename it to "bo" in the next version.

>> +/**
>> + * Driver hook for glEndPerformanceMonitorAMD().
>> + */
>> +static void
>> +brw_end_perf_monitor(struct gl_context *ctx,
>> +                     struct gl_perf_monitor_object *m)
>> +{
>> +   struct brw_context *brw = brw_context(ctx);
>> +   struct brw_perf_monitor_object *monitor = brw_perf_monitor(m);
>> +   if (aggregating_counters_needed(brw, m)) {
>> +      snapshot_aggregating_counters(brw, monitor->gpu_facing_bo,
>> +                                    brw->perfmon.total_counter_size);
>
> At least some variants of the command require 64b alignment -- I'd
> probably stick the ending dump at some fixed offset in the BO, like
> halfway through.

Sounds like a good idea.  It ended up working out, but using a fixed 
2048 byte offset is guaranteed to work out and simplifies things.