-/**
- * Periodic OA samples are read() into these buffer structures via the
- * i915 perf kernel interface and appended to the
- * brw->perfquery.sample_buffers linked list. When we process the
- * results of an OA metrics query we need to consider all the periodic
- * samples between the Begin and End MI_REPORT_PERF_COUNT command
- * markers.
- *
- * 'Periodic' is a simplification as there are other automatic reports
- * written by the hardware also buffered here.
- *
- * Considering three queries, A, B and C:
- *
- * Time ---->
- * ________________A_________________
- * | |
- * | ________B_________ _____C___________
- * | | | | | |
- *
- * And an illustration of sample buffers read over this time frame:
- * [HEAD ][ ][ ][ ][ ][ ][ ][ ][TAIL ]
- *
- * These nodes may hold samples for query A:
- * [ ][ ][ A ][ A ][ A ][ A ][ A ][ ][ ]
- *
- * These nodes may hold samples for query B:
- * [ ][ ][ B ][ B ][ B ][ ][ ][ ][ ]
- *
- * These nodes may hold samples for query C:
- * [ ][ ][ ][ ][ ][ C ][ C ][ C ][ ]
- *
- * The illustration assumes we have an even distribution of periodic
- * samples so all nodes have the same size plotted against time:
- *
- * Note, to simplify code, the list is never empty.
- *
- * With overlapping queries we can see that periodic OA reports may
- * relate to multiple queries and care needs to be take to keep
- * track of sample buffers until there are no queries that might
- * depend on their contents.
- *
- * We use a node ref counting system where a reference ensures that a
- * node and all following nodes can't be freed/recycled until the
- * reference drops to zero.
- *
- * E.g. with a ref of one here:
- * [ 0 ][ 0 ][ 1 ][ 0 ][ 0 ][ 0 ][ 0 ][ 0 ][ 0 ]
- *
- * These nodes could be freed or recycled ("reaped"):
- * [ 0 ][ 0 ]
- *
- * These must be preserved until the leading ref drops to zero:
- * [ 1 ][ 0 ][ 0 ][ 0 ][ 0 ][ 0 ][ 0 ]
- *
- * When a query starts we take a reference on the current tail of
- * the list, knowing that no already-buffered samples can possibly
- * relate to the newly-started query. A pointer to this node is
- * also saved in the query object's ->oa.samples_head.
- *
- * E.g. starting query A while there are two nodes in .sample_buffers:
- * ________________A________
- * |
- *
- * [ 0 ][ 1 ]
- * ^_______ Add a reference and store pointer to node in
- * A->oa.samples_head
- *
- * Moving forward to when the B query starts with no new buffer nodes:
- * (for reference, i915 perf reads() are only done when queries finish)
- * ________________A_______
- * | ________B___
- * | |
- *
- * [ 0 ][ 2 ]
- * ^_______ Add a reference and store pointer to
- * node in B->oa.samples_head
- *
- * Once a query is finished, after an OA query has become 'Ready',
- * once the End OA report has landed and after we we have processed
- * all the intermediate periodic samples then we drop the
- * ->oa.samples_head reference we took at the start.
- *
- * So when the B query has finished we have:
- * ________________A________
- * | ______B___________
- * | | |
- * [ 0 ][ 1 ][ 0 ][ 0 ][ 0 ]
- * ^_______ Drop B->oa.samples_head reference
- *
- * We still can't free these due to the A->oa.samples_head ref:
- * [ 1 ][ 0 ][ 0 ][ 0 ]
- *
- * When the A query finishes: (note there's a new ref for C's samples_head)
- * ________________A_________________
- * | |
- * | _____C_________
- * | | |
- * [ 0 ][ 0 ][ 0 ][ 0 ][ 1 ][ 0 ][ 0 ]
- * ^_______ Drop A->oa.samples_head reference
- *
- * And we can now reap these nodes up to the C->oa.samples_head:
- * [ X ][ X ][ X ][ X ]
- * keeping -> [ 1 ][ 0 ][ 0 ]
- *
- * We reap old sample buffers each time we finish processing an OA
- * query by iterating the sample_buffers list from the head until we
- * find a referenced node and stop.
- *
- * Reaped buffers move to a perfquery.free_sample_buffers list and
- * when we come to read() we first look to recycle a buffer from the
- * free_sample_buffers list before allocating a new buffer.
- */
-struct oa_sample_buf {
- struct exec_node link;
- int refcount;
- int len;
- uint8_t buf[I915_PERF_OA_SAMPLE_SIZE * 10];
- uint32_t last_timestamp;