[Mesa-dev] [PATCH 04/51] i965: Share the workaround bo between all contexts

[Chris Wilson]

Since the workaround bo is used strictly as a write-only buffer, we need
only allocate one per screen and use the same one from all contexts.

(The caveat here is during extension initialisation, where we write into
and read back register values from the buffer, but that is performed only
once for the first context - and baring synchronisation issues should not
be a problem. Safer would be to move that also to the screen.)

v2: Give the workaround bo its own init function and don't piggy back
intel_bufmgr_init() since it is not that related.

v3: Drop the reference count of the workaround bo for the context since
the context itself is owned by the screen (and so we can rely on the bo
existing for the lifetime of the context).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Kenneth Graunke <kenneth at whitecape.org>
Cc: Martin Peres <martin.peres at linux.intel.com>
---
 src/mesa/drivers/dri/i965/brw_context.h      |  2 +-
 src/mesa/drivers/dri/i965/brw_pipe_control.c | 12 +++++-------
 src/mesa/drivers/dri/i965/intel_screen.c     | 15 +++++++++++++++
 src/mesa/drivers/dri/i965/intel_screen.h     |  1 +
 4 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_context.h b/src/mesa/drivers/dri/i965/brw_context.h
index d14369a531..28290d85f1 100644
--- a/src/mesa/drivers/dri/i965/brw_context.h
+++ b/src/mesa/drivers/dri/i965/brw_context.h
@@ -1735,7 +1735,7 @@ gen9_use_linear_1d_layout(const struct brw_context *brw,
 
 /* brw_pipe_control.c */
 int brw_init_pipe_control(struct brw_context *brw,
-			  const struct gen_device_info *info);
+                          const struct gen_device_info *info);
 void brw_fini_pipe_control(struct brw_context *brw);
 
 void brw_emit_pipe_control_flush(struct brw_context *brw, uint32_t flags);
diff --git a/src/mesa/drivers/dri/i965/brw_pipe_control.c b/src/mesa/drivers/dri/i965/brw_pipe_control.c
index b8f740640f..22c946f744 100644
--- a/src/mesa/drivers/dri/i965/brw_pipe_control.c
+++ b/src/mesa/drivers/dri/i965/brw_pipe_control.c
@@ -371,20 +371,18 @@ brw_init_pipe_control(struct brw_context *brw,
    /* We can't just use brw_state_batch to get a chunk of space for
     * the gen6 workaround because it involves actually writing to
     * the buffer, and the kernel doesn't let us write to the batch.
+    *
+    * As the screen has a long lifetime than the contexts derived from
+    * it, we do not need to add our own reference count and can simply
+    * rely on the bo always existing for the duration of the context.
     */
-   brw->workaround_bo = drm_intel_bo_alloc(brw->bufmgr,
-                                           "pipe_control workaround",
-                                           4096, 4096);
-   if (brw->workaround_bo == NULL)
-      return -ENOMEM;
+   brw->workaround_bo = brw->screen->workaround_bo;
 
    brw->pipe_controls_since_last_cs_stall = 0;
-
    return 0;
 }
 
 void
 brw_fini_pipe_control(struct brw_context *brw)
 {
-   drm_intel_bo_unreference(brw->workaround_bo);
 }
diff --git a/src/mesa/drivers/dri/i965/intel_screen.c b/src/mesa/drivers/dri/i965/intel_screen.c
index c79268f71b..c4b205cd80 100644
--- a/src/mesa/drivers/dri/i965/intel_screen.c
+++ b/src/mesa/drivers/dri/i965/intel_screen.c
@@ -1024,6 +1024,7 @@ intelDestroyScreen(__DRIscreen * sPriv)
 {
    struct intel_screen *screen = sPriv->driverPrivate;
 
+   drm_intel_bo_unreference(screen->workaround_bo);
    dri_bufmgr_destroy(screen->bufmgr);
    driDestroyOptionInfo(&screen->optionCache);
 
@@ -1204,6 +1205,17 @@ intel_init_bufmgr(struct intel_screen *screen)
 }
 
 static bool
+intel_init_workaround_bo(struct intel_screen *screen)
+{
+   /* A small scratch bo shared by all contexts, primarily used
+    * for doing PIPECONTROL serialisation writes that are discarded.
+    */
+   screen->workaround_bo =
+      drm_intel_bo_alloc(screen->bufmgr, "pipe_control w/a", 4096, 4096);
+   return screen->workaround_bo != NULL;
+}
+
+static bool
 intel_detect_swizzling(struct intel_screen *screen)
 {
    drm_intel_bo *buffer;
@@ -1669,6 +1681,9 @@ __DRIconfig **intelInitScreen2(__DRIscreen *dri_screen)
    if (!intel_init_bufmgr(screen))
        return false;
 
+   if (!intel_init_workaround_bo(screen))
+       return false;
+
    screen->deviceID = drm_intel_bufmgr_gem_get_devid(screen->bufmgr);
    if (!gen_get_device_info(screen->deviceID, &screen->devinfo))
       return false;
diff --git a/src/mesa/drivers/dri/i965/intel_screen.h b/src/mesa/drivers/dri/i965/intel_screen.h
index 890dd9044b..0fb83e724f 100644
--- a/src/mesa/drivers/dri/i965/intel_screen.h
+++ b/src/mesa/drivers/dri/i965/intel_screen.h
@@ -74,6 +74,7 @@ struct intel_screen
 #define KERNEL_ALLOWS_COMPUTE_DISPATCH              (1<<4)
 
    dri_bufmgr *bufmgr;
+   drm_intel_bo *workaround_bo;
 
    /**
     * A unique ID for shader programs.
-- 
2.11.0