[Intel-gfx] [PATCH] drm/i915/perf: Fix OA context id overlap with idle context id

[Umesh Nerlige Ramappa]

On Mon, Jan 27, 2020 at 11:16:32AM +0200, Lionel Landwerlin wrote:

[snip]

>>>>--- a/drivers/gpu/drm/i915/i915_perf.c
>>>>+++ b/drivers/gpu/drm/i915/i915_perf.c
>>>>@@ -1323,7 +1323,12 @@ static int oa_get_render_ctx_id(struct 
>>>>i915_perf_stream *stream)
>>>>     case 12: {
>>>>         stream->specific_ctx_id_mask =
>>>>             ((1U << GEN11_SW_CTX_ID_WIDTH) - 1) << 
>>>>(GEN11_SW_CTX_ID_SHIFT - 32);
>>>>-        stream->specific_ctx_id = stream->specific_ctx_id_mask;
>>>>+        /* Pick an unused context id
>>>>+         * 0 - (NUM_CONTEXT_TAG - 1) are used by other contexts
>>>>+         * GEN12_MAX_CONTEXT_HW_ID (0x7ff) is used by idle context
>>>>+         */
>>>>+        stream->specific_ctx_id = (GEN12_MAX_CONTEXT_HW_ID - 1) 
>>>><< (GEN11_SW_CTX_ID_SHIFT - 32);
>>>>+        BUILD_BUG_ON((GEN12_MAX_CONTEXT_HW_ID - 1) < NUM_CONTEXT_TAG);
>>>
>>>
>>>Arg yeah, we can't use an id that has all bits to 1 because that 
>>>matches the idle value in the OA reports :/
>>>
>>>This also affects gen8-10 cases (afaik).
>>
>>For gen8-10, I did not see a specific definition for an idle context 
>>id.  The from/to idle context switches are indicated by dedicated 
>>bits in the CSB instead (from spec).
>
>
>I meant that I remember the periodic OA reports when HW is idle to 
>have the contex_id=0xffffffff.

For these gens we use 0x1fffff as the context id. Before we return 
reports to the user, we are setting context id to 0xffffffff for invalid 
and irrelevant contexts.

Thanks,
Umesh
>
>I could remember wrong :/
>
>
>-Lionel
>
>
>>
>>Thanks,
>>Umesh
>>
>>>
>>>
>>>Thanks for spotting this!
>>>
>>>
>>>-Lionel
>>>
>>>
>>>>         break;
>>>>     }
>>>>@@ -1331,7 +1336,7 @@ static int oa_get_render_ctx_id(struct 
>>>>i915_perf_stream *stream)
>>>>         MISSING_CASE(INTEL_GEN(ce->engine->i915));
>>>>     }
>>>>-    ce->tag = stream->specific_ctx_id_mask;
>>>>+    ce->tag = stream->specific_ctx_id;
>>>>     DRM_DEBUG_DRIVER("filtering on ctx_id=0x%x ctx_id_mask=0x%x\n",
>>>>              stream->specific_ctx_id,
>>>
>>>
>