Mesa (master): iris: Add batch-local synchronization book-keeping to iris_bo.

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Module: Mesa
Branch: master
Commit: 7878cbec59a394904feb512ab6a756a27242912d
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=7878cbec59a394904feb512ab6a756a27242912d

Author: Francisco Jerez <currojerez at riseup.net>
Date:   Thu Apr 23 17:56:11 2020 -0700

iris: Add batch-local synchronization book-keeping to iris_bo.

The purpose of this is to represent the cache coherency state of a
buffer as a vector of integers (AKA seqnos), one for each incoherent
caching domain of the GPU.  A seqno will identify a single section of
a batch buffer uniquely across the whole pipe_screen (which means that
there will be no ambiguity about what context a given seqno belongs to
even if there are multiple threads accessing the same buffer in
parallel), and is guaranteed to be allocated in monotonically
increasing order within any given context.  The iris_bo_bump_seqno()
helper is provided for marking the last update of a buffer from a
given caching domain in a lockless manner.

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3875>

---

 src/gallium/drivers/iris/iris_bufmgr.h | 55 ++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/src/gallium/drivers/iris/iris_bufmgr.h b/src/gallium/drivers/iris/iris_bufmgr.h
index 6ae559805bc..2966d993ff6 100644
--- a/src/gallium/drivers/iris/iris_bufmgr.h
+++ b/src/gallium/drivers/iris/iris_bufmgr.h
@@ -89,6 +89,34 @@ enum iris_memory_zone {
 #define IRIS_BORDER_COLOR_POOL_ADDRESS IRIS_MEMZONE_DYNAMIC_START
 #define IRIS_BORDER_COLOR_POOL_SIZE (64 * 1024)
 
+/**
+ * Classification of the various incoherent caches of the GPU into a number of
+ * caching domains.
+ */
+enum iris_domain {
+   /** Render color cache. */
+   IRIS_DOMAIN_RENDER_WRITE = 0,
+   /** (Hi)Z/stencil cache. */
+   IRIS_DOMAIN_DEPTH_WRITE,
+   /** Any other read-write cache. */
+   IRIS_DOMAIN_OTHER_WRITE,
+   /** Any other read-only cache. */
+   IRIS_DOMAIN_OTHER_READ,
+   /** Number of caching domains. */
+   NUM_IRIS_DOMAINS,
+   /** Not a real cache, use to opt out of the cache tracking mechanism. */
+   IRIS_DOMAIN_NONE = NUM_IRIS_DOMAINS
+};
+
+/**
+ * Whether a caching domain is guaranteed not to write any data to memory.
+ */
+static inline bool
+iris_domain_is_read_only(enum iris_domain access)
+{
+   return access == IRIS_DOMAIN_OTHER_READ;
+}
+
 struct iris_bo {
    /**
     * Size in bytes of the buffer object.
@@ -165,6 +193,15 @@ struct iris_bo {
    /** BO cache list */
    struct list_head head;
 
+   /**
+    * Synchronization sequence number of most recent access of this BO from
+    * each caching domain.
+    *
+    * Although this is a global field, use in multiple contexts should be
+    * safe, see iris_emit_buffer_barrier_for() for details.
+    */
+   uint64_t last_seqnos[NUM_IRIS_DOMAINS];
+
    /**
     * Boolean of whether the GPU is definitely not accessing the buffer.
     *
@@ -377,6 +414,24 @@ iris_bo_offset_from_base_address(struct iris_bo *bo)
    return bo->gtt_offset;
 }
 
+/**
+ * Track access of a BO from the specified caching domain and sequence number.
+ *
+ * Can be used without locking.  Only the most recent access (i.e. highest
+ * seqno) is tracked.
+ */
+static inline void
+iris_bo_bump_seqno(struct iris_bo *bo, uint64_t seqno,
+                   enum iris_domain type)
+{
+   uint64_t *const last_seqno = &bo->last_seqnos[type];
+   uint64_t tmp, prev_seqno = p_atomic_read(last_seqno);
+
+   while (prev_seqno < seqno &&
+          prev_seqno != (tmp = p_atomic_cmpxchg(last_seqno, prev_seqno, seqno)))
+      prev_seqno = tmp;
+}
+
 enum iris_memory_zone iris_memzone_for_address(uint64_t address);
 
 #endif /* IRIS_BUFMGR_H */