radeonsi: implement mechanism for IBs without partial flushes at the end (v6)

(This patch doesn't enable the behavior. It will be enabled in a later
commit.)

Draw calls from multiple IBs can be executed in parallel.

v2: do emit partial flushes on SI
v3: invalidate all shader caches at the beginning of IBs
v4: don't call si_emit_cache_flush in si_flush_gfx_cs if not needed,
    only do this for flushes invoked internally
v5: empty IBs should wait for idle if the flush requires it
v6: split the commit

If we artificially limit the number of draw calls per IB to 5, we'll get
a lot more IBs, leading to a lot more partial flushes. Let's see how
the removal of partial flushes changes GPU utilization in that scenario:

With partial flushes (time busy):
    CP: 99%
    SPI: 86%
    CB: 73:

Without partial flushes (time busy):
    CP: 99%
    SPI: 93%
    CB: 81%

Tested-by: Benedikt Schemmer <ben@besd.de>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

diff --git a/src/gallium/drivers/radeon/radeon_winsys.h b/src/gallium/drivers/radeon/radeon_winsys.h
index 157b2e405504957391c3d8ec40d721e95b485274..fae4fb7a95d8ffa7b81161be3ef274959b4b38eb 100644 (file)
--- a/src/gallium/drivers/radeon/radeon_winsys.h
+++ b/src/gallium/drivers/radeon/radeon_winsys.h
@@ -28,6 +28,13 @@
 
 /* The public winsys interface header for the radeon driver. */
 
+/* Whether the next IB can start immediately and not wait for draws and
+ * dispatches from the current IB to finish. */
+#define RADEON_FLUSH_START_NEXT_GFX_IB_NOW     (1u << 31)
+
+#define RADEON_FLUSH_ASYNC_START_NEXT_GFX_IB_NOW \
+       (PIPE_FLUSH_ASYNC | RADEON_FLUSH_START_NEXT_GFX_IB_NOW)
+
 #include "pipebuffer/pb_buffer.h"
 
 #include "amd/common/ac_gpu_info.h"

diff --git a/src/gallium/drivers/radeonsi/si_gfx_cs.c b/src/gallium/drivers/radeonsi/si_gfx_cs.c
index b1ed620b0c651ea0e817afff4c7bcdb83c629c44..147433b69b67e30e33dab2167f010b1f5f0050ac 100644 (file)
--- a/src/gallium/drivers/radeonsi/si_gfx_cs.c
+++ b/src/gallium/drivers/radeonsi/si_gfx_cs.c
@@ -69,11 +69,28 @@ void si_flush_gfx_cs(struct si_context *ctx, unsigned flags,
 {
        struct radeon_winsys_cs *cs = ctx->gfx_cs;
        struct radeon_winsys *ws = ctx->ws;
+       unsigned wait_flags = 0;
 
        if (ctx->gfx_flush_in_progress)
                return;
 
-       if (!radeon_emitted(cs, ctx->initial_gfx_cs_size))
+       if (ctx->chip_class == VI && ctx->screen->info.drm_minor <= 1) {
+               /* DRM 3.1.0 doesn't flush TC for VI correctly. */
+               wait_flags |= SI_CONTEXT_PS_PARTIAL_FLUSH |
+                             SI_CONTEXT_CS_PARTIAL_FLUSH |
+                             SI_CONTEXT_INV_GLOBAL_L2;
+       } else if (ctx->chip_class == SI) {
+               /* The kernel flushes L2 before shaders are finished. */
+               wait_flags |= SI_CONTEXT_PS_PARTIAL_FLUSH |
+                             SI_CONTEXT_CS_PARTIAL_FLUSH;
+       } else if (!(flags & RADEON_FLUSH_START_NEXT_GFX_IB_NOW)) {
+               wait_flags |= SI_CONTEXT_PS_PARTIAL_FLUSH |
+                             SI_CONTEXT_CS_PARTIAL_FLUSH;
+       }
+
+       /* Drop this flush if it's a no-op. */
+       if (!radeon_emitted(cs, ctx->initial_gfx_cs_size) &&
+           (!wait_flags || !ctx->gfx_last_ib_is_busy))
                return;
 
        if (si_check_device_reset(ctx))
@@ -103,20 +120,17 @@ void si_flush_gfx_cs(struct si_context *ctx, unsigned flags,
                ctx->streamout.suspended = true;
        }
 
-       ctx->flags |= SI_CONTEXT_CS_PARTIAL_FLUSH |
-                       SI_CONTEXT_PS_PARTIAL_FLUSH;
-
-       /* DRM 3.1.0 doesn't flush TC for VI correctly. */
-       if (ctx->chip_class == VI && ctx->screen->info.drm_minor <= 1)
-               ctx->flags |= SI_CONTEXT_INV_GLOBAL_L2 |
-                               SI_CONTEXT_INV_VMEM_L1;
-
        /* Make sure CP DMA is idle at the end of IBs after L2 prefetches
         * because the kernel doesn't wait for it. */
        if (ctx->chip_class >= CIK)
                si_cp_dma_wait_for_idle(ctx);
 
-       si_emit_cache_flush(ctx);
+       /* Wait for draw calls to finish if needed. */
+       if (wait_flags) {
+               ctx->flags |= wait_flags;
+               si_emit_cache_flush(ctx);
+       }
+       ctx->gfx_last_ib_is_busy = wait_flags == 0;
 
        if (ctx->current_saved_cs) {
                si_trace_emit(ctx);
@@ -189,12 +203,21 @@ void si_begin_new_gfx_cs(struct si_context *ctx)
        if (ctx->is_debug)
                si_begin_gfx_cs_debug(ctx);
 
-       /* Flush read caches at the beginning of CS not flushed by the kernel. */
-       if (ctx->chip_class >= CIK)
-               ctx->flags |= SI_CONTEXT_INV_SMEM_L1 |
-                               SI_CONTEXT_INV_ICACHE;
-
-       ctx->flags |= SI_CONTEXT_START_PIPELINE_STATS;
+       /* Always invalidate caches at the beginning of IBs, because external
+        * users (e.g. BO evictions and SDMA/UVD/VCE IBs) can modify our
+        * buffers.
+        *
+        * Note that the cache flush done by the kernel at the end of GFX IBs
+        * isn't useful here, because that flush can finish after the following
+        * IB starts drawing.
+        *
+        * TODO: Do we also need to invalidate CB & DB caches?
+        */
+       ctx->flags |= SI_CONTEXT_INV_ICACHE |
+                     SI_CONTEXT_INV_SMEM_L1 |
+                     SI_CONTEXT_INV_VMEM_L1 |
+                     SI_CONTEXT_INV_GLOBAL_L2 |
+                     SI_CONTEXT_START_PIPELINE_STATS;
 
        /* set all valid group as dirty so they get reemited on
         * next draw command

diff --git a/src/gallium/drivers/radeonsi/si_pipe.h b/src/gallium/drivers/radeonsi/si_pipe.h
index 3a2f7ca11d110b3e98904cd14fb8be78fdbae1a4..125b3a72bfb96670efe5daf3a0a3742e2b1baf02 100644 (file)
--- a/src/gallium/drivers/radeonsi/si_pipe.h
+++ b/src/gallium/drivers/radeonsi/si_pipe.h
@@ -559,6 +559,7 @@ struct si_context {
        uint16_t                        prefetch_L2_mask;
 
        bool                            gfx_flush_in_progress:1;
+       bool                            gfx_last_ib_is_busy:1;
        bool                            compute_is_busy:1;
 
        unsigned                        num_gfx_cs_flushes;