[Mesa-dev] [PATCH 4/9] intel: Don't flush the old context in intelMakeCurrent

[Adam Jackson]

From: Neil Roberts <neil at linux.intel.com>

It shouldn't be necessary to flush the context within the driver
implementation because the old context is explicitly flushed in
_mesa_make_current which is called a little further on. It is useful to
only have a single place that flushes when switching contexts to make it
easier to later implement the GL_KHR_context_flush_control extension.

The flush in intelMakeCurrent was added in commit 5505865 to implement
the GLX semantics that the context should be flushed when it is
released.  When the commit was made there was no flush in
_mesa_make_current because it was only added later in 93102b4c. I think
that later commit effectively makes the first commit redundant.

The later commit was added because it looks like the flush in
intelMakeCurrent is actually not even hit anymore. This is because when
a new context is bound the old context is usually unbound first in
MakeContextCurrent and dri2_make_current. Since commit b4bb668020 the
unbind implementations call _mesa_make_current(NULL) which effectively
means that there should almost never be a current context when
intelMakeCurrent is called.

However one caveat with that is that MakeContextCurrent doesn't call the
unbind virtual if the context is still bound in another thread. It seems
to me like this is a bug anyway because the call to
_mesa_make_current(NULL) was added to fix a problem where the bind
implementation can incorrectly think the context is already bound when
switching to an indirect context and back.  Presumably this bug will
still happen if you do that while the context is bound in another
thread.

I don't think it should make any difference anyway if the flush is moved
lower in intelMakeCurrent because all of the code between the original
flush and the call to _mesa_make_current looks quite trivial and it only
operates on the new context not the old one.
---
 src/mesa/drivers/dri/i915/intel_context.c | 9 ---------
 src/mesa/drivers/dri/i965/brw_context.c   | 9 ---------
 2 files changed, 18 deletions(-)

diff --git a/src/mesa/drivers/dri/i915/intel_context.c b/src/mesa/drivers/dri/i915/intel_context.c
index 5618dcd..f7c82e8 100644
--- a/src/mesa/drivers/dri/i915/intel_context.c
+++ b/src/mesa/drivers/dri/i915/intel_context.c
@@ -621,21 +621,12 @@ intelMakeCurrent(__DRIcontext * driContextPriv,
                  __DRIdrawable * driReadPriv)
 {
    struct intel_context *intel;
-   GET_CURRENT_CONTEXT(curCtx);
 
    if (driContextPriv)
       intel = (struct intel_context *) driContextPriv->driverPrivate;
    else
       intel = NULL;
 
-   /* According to the glXMakeCurrent() man page: "Pending commands to
-    * the previous context, if any, are flushed before it is released."
-    * But only flush if we're actually changing contexts.
-    */
-   if (intel_context(curCtx) && intel_context(curCtx) != intel) {
-      _mesa_flush(curCtx);
-   }
-
    if (driContextPriv) {
       struct gl_context *ctx = &intel->ctx;
       struct gl_framebuffer *fb, *readFb;
diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index fb68f55..cbb3087 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -1058,21 +1058,12 @@ intelMakeCurrent(__DRIcontext * driContextPriv,
                  __DRIdrawable * driReadPriv)
 {
    struct brw_context *brw;
-   GET_CURRENT_CONTEXT(curCtx);
 
    if (driContextPriv)
       brw = (struct brw_context *) driContextPriv->driverPrivate;
    else
       brw = NULL;
 
-   /* According to the glXMakeCurrent() man page: "Pending commands to
-    * the previous context, if any, are flushed before it is released."
-    * But only flush if we're actually changing contexts.
-    */
-   if (brw_context(curCtx) && brw_context(curCtx) != brw) {
-      _mesa_flush(curCtx);
-   }
-
    if (driContextPriv) {
       struct gl_context *ctx = &brw->ctx;
       struct gl_framebuffer *fb, *readFb;
-- 
2.4.0