i915 perf stream format

The stream is made of records that all have the same header:

struct i915_perf_record_header {
	uint32_t type;
	uint16_t pad;
	uint16_t size;
};

Most records are of type DRM_I915_PERF_RECORD_SAMPLE and contain the metrics we're interested in capturing. Other record types are DRM_I915_PERF_RECORD_OA_REPORT_LOST - signalling that the hardware had to drop an OA report and DRM_I915_PERF_RECORD_OA_BUFFER_OVERFLOW - signalling that the circular OA buffer that the hardware writes OA reports into has filled.

header->size is the total size of the record, including the size of the struct i915_perf_record_header.

The contents of sample records, following the header, are configurable via the properties given to the DRM_IOCTL_I915_PERF_OPEN ioctl when opening a stream. The boolean DRM_I915_PERF_PROP_SAMPLE_xyz properties control what's included in a stream's sample records. The relative order of data within a sample is predefined and documented in the i915_drm.h header. DRM_I915_PERF_PROP_SAMPLE_OA_REPORT requests i915 perf to forward raw OA snapshots as part of the sample payload. Each optional sub record of data that can be added to a sample payload can be expected to be 8 byte aligned.

The hardware can write raw OA counter snapshots in a number of formats with different sizes. Currently we're mostly just using the largest, 256 byte, formats I915_OA_FORMAT_A45_B8_C8 on Haswell or I915_OA_FORMAT_A32u40_A4u32_B8_C8 on Broadwell+

I915_OA_FORMAT_A45_B8_C8

Byte Offset	Counter
0	Report ID / Reason
4	Timestamp
8	Undefined
12	Aggregate Counter 0
16	Aggregate Counter 1
20	Aggregate Counter 2
24	Aggregate Counter 3
28	Aggregate Counter 4
32	Aggregate Counter 5
36	Aggregate Counter 6
40	Aggregate Counter 7
44	Aggregate Counter 8
48	Aggregate Counter 9
52	Aggregate Counter 10
56	Aggregate Counter 11
60	Aggregate Counter 12
64	Aggregate Counter 13
68	Aggregate Counter 14
72	Aggregate Counter 15
76	Aggregate Counter 16
80	Aggregate Counter 17
84	Aggregate Counter 18
88	Aggregate Counter 19
92	Aggregate Counter 20
96	Aggregate Counter 21
100	Aggregate Counter 22
104	Aggregate Counter 23
108	Aggregate Counter 24
112	Aggregate Counter 25
116	Aggregate Counter 26
120	Aggregate Counter 27
124	Aggregate Counter 28
128	Aggregate Counter 29
132	Aggregate Counter 30
136	Aggregate Counter 31
140	Aggregate Counter 32
144	Aggregate Counter 33
148	Aggregate Counter 34
152	Aggregate Counter 35
156	Aggregate Counter 36
160	Aggregate Counter 37
164	Aggregate Counter 38
168	Aggregate Counter 39
172	Aggregate Counter 40
176	Aggregate Counter 41
180	Aggregate Counter 42
184	Aggregate Counter 43
188	Aggregate Counter 44
192	Boolean Counter 0
196	Boolean Counter 1
200	Boolean Counter 2
204	Boolean Counter 3
208	Boolean Counter 4
212	Boolean Counter 5
216	Boolean Counter 6
220	Boolean Counter 7
224	Custom Counter 0
228	Custom Counter 1
232	Custom Counter 2
236	Custom Counter 3
240	Custom Counter 4
244	Custom Counter 5
248	Custom Counter 6
252	Custom Counter 7

I915_OA_FORMAT_A32u40_A4u32_B8_C8

Byte Offset	Counter
0	Report ID / Reason
4	Timestamp
8	Context ID
12	GPU Clock Ticks
16	40 bit Aggregate Counter 0 least significant 32 bits
20	40 bit Aggregate Counter 1 least significant 32 bits
24	40 bit Aggregate Counter 2 least significant 32 bits
28	40 bit Aggregate Counter 3 least significant 32 bits
32	40 bit Aggregate Counter 4 least significant 32 bits
36	40 bit Aggregate Counter 5 least significant 32 bits
40	40 bit Aggregate Counter 6 least significant 32 bits
44	40 bit Aggregate Counter 7 least significant 32 bits
48	40 bit Aggregate Counter 8 least significant 32 bits
52	40 bit Aggregate Counter 9 least significant 32 bits
56	40 bit Aggregate Counter 10 least significant 32 bits
60	40 bit Aggregate Counter 11 least significant 32 bits
64	40 bit Aggregate Counter 12 least significant 32 bits
68	40 bit Aggregate Counter 13 least significant 32 bits
72	40 bit Aggregate Counter 14 least significant 32 bits
76	40 bit Aggregate Counter 15 least significant 32 bits
80	40 bit Aggregate Counter 16 least significant 32 bits
84	40 bit Aggregate Counter 17 least significant 32 bits
88	40 bit Aggregate Counter 18 least significant 32 bits
92	40 bit Aggregate Counter 19 least significant 32 bits
96	40 bit Aggregate Counter 20 least significant 32 bits
100	40 bit Aggregate Counter 21 least significant 32 bits
104	40 bit Aggregate Counter 22 least significant 32 bits
108	40 bit Aggregate Counter 23 least significant 32 bits
112	40 bit Aggregate Counter 24 least significant 32 bits
116	40 bit Aggregate Counter 25 least significant 32 bits
120	40 bit Aggregate Counter 26 least significant 32 bits
124	40 bit Aggregate Counter 27 least significant 32 bits
128	40 bit Aggregate Counter 28 least significant 32 bits
132	40 bit Aggregate Counter 29 least significant 32 bits
136	40 bit Aggregate Counter 30 least significant 32 bits
140	40 bit Aggregate Counter 31 least significant 32 bits
144	32 bit Aggregate Counter 32
148	32 bit Aggregate Counter 33
152	32 bit Aggregate Counter 34
156	32 bit Aggregate Counter 35
160	40 bit Aggregate Counter 0 most significant 8 bits
161	40 bit Aggregate Counter 1 most significant 8 bits
162	40 bit Aggregate Counter 2 most significant 8 bits
163	40 bit Aggregate Counter 3 most significant 8 bits
164	40 bit Aggregate Counter 4 most significant 8 bits
165	40 bit Aggregate Counter 5 most significant 8 bits
166	40 bit Aggregate Counter 6 most significant 8 bits
167	40 bit Flexible, Aggregate EU Counter 7 most significant 8 bits
168	40 bit Flexible, Aggregate EU Counter 8 most significant 8 bits
169	40 bit Flexible, Aggregate EU Counter 9 most significant 8 bits
170	40 bit Flexible, Aggregate EU Counter 10 most significant 8 bits
171	40 bit Flexible, Aggregate EU Counter 11 most significant 8 bits
172	40 bit Flexible, Aggregate EU Counter 12 most significant 8 bits
173	40 bit Flexible, Aggregate EU Counter 13 most significant 8 bits
174	40 bit Flexible, Aggregate EU Counter 14 most significant 8 bits
175	40 bit Flexible, Aggregate EU Counter 15 most significant 8 bits
176	40 bit Flexible, Aggregate EU Counter 16 most significant 8 bits
177	40 bit Flexible, Aggregate EU Counter 17 most significant 8 bits
178	40 bit Flexible, Aggregate EU Counter 18 most significant 8 bits
179	40 bit Flexible, Aggregate EU Counter 19 most significant 8 bits
180	40 bit Flexible, Aggregate EU Counter 20 most significant 8 bits
181	40 bit Aggregate Counter 21 most significant 8 bits
182	40 bit Aggregate Counter 22 most significant 8 bits
183	40 bit Aggregate Counter 23 most significant 8 bits
184	40 bit Aggregate Counter 24 most significant 8 bits
185	40 bit Aggregate Counter 25 most significant 8 bits
186	40 bit Aggregate Counter 26 most significant 8 bits
187	40 bit Aggregate Counter 27 most significant 8 bits
188	40 bit Aggregate Counter 28 most significant 8 bits
189	40 bit Aggregate Counter 29 most significant 8 bits
190	40 bit Aggregate Counter 30 most significant 8 bits
191	40 bit Aggregate Counter 31 most significant 8 bits
192	Boolean Counter 0
196	Boolean Counter 1
200	Boolean Counter 2
204	Boolean Counter 3
208	Boolean Counter 4
212	Boolean Counter 5
216	Boolean Counter 6
220	Boolean Counter 7
224	Custom Counter 0
228	Custom Counter 1
232	Custom Counter 2
236	Custom Counter 3
240	Custom Counter 4
244	Custom Counter 5
248	Custom Counter 6
252	Custom Counter 7

On Broadwell+ the 32 bit Reason field bits 24:19 represent what triggered the report. This reason is represented with mutually exclusive flags:

Flag Bit	Reason
0	Timer triggered sample
1	Internal report trigger 1
2	Internal report trigger 2
3	Context switch
4	GO transition from 1 to 0
5	Clock ratio change between squashed Slice Clock frequency and squashed Unslice clock frequency