[Mesa-dev] [PATCH 30/53] mesa: don't always set _NEW_PROGRAM when linking
Timothy Arceri
timothy.arceri at collabora.com
Tue Jan 3 23:36:48 UTC 2017
On Tue, 2017-01-03 at 23:55 +0100, Marek Olšák wrote:
> On Tue, Jan 3, 2017 at 11:14 PM, Timothy Arceri
> <timothy.arceri at collabora.com> wrote:
> > On Tue, 2017-01-03 at 22:41 +0100, Marek Olšák wrote:
> > > On Tue, Jan 3, 2017 at 10:14 PM, Timothy Arceri
> > > <timothy.arceri at collabora.com> wrote:
> > > > On Tue, 2017-01-03 at 22:07 +0100, Marek Olšák wrote:
> > > > > On Tue, Jan 3, 2017 at 9:57 PM, Timothy Arceri
> > > > > <timothy.arceri at collabora.com> wrote:
> > > > > > On Tue, 2017-01-03 at 20:47 +0100, Marek Olšák wrote:
> > > > > > > On Tue, Jan 3, 2017 at 3:43 AM, Timothy Arceri
> > > > > > > <timothy.arceri at collabora.com> wrote:
> > > > > > > > We only need to set it when linking was successful and
> > > > > > > > the
> > > > > > > > program
> > > > > > > > being linked is currently active.
> > > > > > > >
> > > > > > > > The programs_in_use mask is just used as a flag for now
> > > > > > > > but
> > > > > > > > in
> > > > > > > > a following patch we will use it to update the
> > > > > > > > CurrentProgram
> > > > > > > > array.
> > > > > > > > ---
> > > > > > > > src/mesa/main/shaderapi.c | 22 +++++++++++++++++++++-
> > > > > > > > 1 file changed, 21 insertions(+), 1 deletion(-)
> > > > > > > >
> > > > > > > > diff --git a/src/mesa/main/shaderapi.c
> > > > > > > > b/src/mesa/main/shaderapi.c
> > > > > > > > index 022afab..6c03dcb 100644
> > > > > > > > --- a/src/mesa/main/shaderapi.c
> > > > > > > > +++ b/src/mesa/main/shaderapi.c
> > > > > > > > @@ -1083,10 +1083,30 @@ _mesa_link_program(struct
> > > > > > > > gl_context
> > > > > > > > *ctx,
> > > > > > > > struct gl_shader_program *shProg)
> > > > > > > > return;
> > > > > > > > }
> > > > > > > >
> > > > > > > > - FLUSH_VERTICES(ctx, _NEW_PROGRAM);
> > > > > > > > + unsigned programs_in_use = 0;
> > > > > > > > + if (ctx->_Shader)
> > > > > > > > + for (unsigned stage = 0; stage <
> > > > > > > > MESA_SHADER_STAGES;
> > > > > > > > stage++) {
> > > > > > > > + if (ctx->_Shader->CurrentProgram[stage] ==
> > > > > > > > shProg) {
> > > > > > > > + programs_in_use |= 1 << stage;
> > > > > > > > + }
> > > > > > > > + }
> > > > > > > >
> > > > > > > > _mesa_glsl_link_shader(ctx, shProg);
> > > > > > > >
> > > > > > > > + /* From section 7.3 (Program Objects) of the OpenGL
> > > > > > > > 4.5
> > > > > > > > spec:
> > > > > > > > + *
> > > > > > > > + * "If LinkProgram or ProgramBinary successfully
> > > > > > > > re-
> > > > > > > > links a
> > > > > > > > program
> > > > > > > > + * object that is active for any shader stage,
> > > > > > > > then
> > > > > > > > the
> > > > > > > > newly generated
> > > > > > > > + * executable code will be installed as part of
> > > > > > > > the
> > > > > > > > current
> > > > > > > > rendering
> > > > > > > > + * state for all shader stages where the
> > > > > > > > program is
> > > > > > > > active.
> > > > > > > > + * Additionally, the newly generated executable
> > > > > > > > code is
> > > > > > > > made part of
> > > > > > > > + * the state of any program pipeline for all
> > > > > > > > stages
> > > > > > > > where
> > > > > > > > the program
> > > > > > > > + * is attached."
> > > > > > > > + */
> > > > > > > > + if (shProg->data->LinkStatus && programs_in_use) {
> > > > > > > > + FLUSH_VERTICES(ctx, _NEW_PROGRAM);
> > > > > > > > + }
> > > > > > >
> > > > > > > This doesn't seem correct. If the context has unflushed
> > > > > > > vertices,
> > > > > > > calling FLUSH_VERTICES after linking will use the new
> > > > > > > linked
> > > > > > > program
> > > > > > > instead of the previous program for which the vertices
> > > > > > > were
> > > > > > > submitted.
> > > > > >
> > > > > > Your probably right but this doesn't make anything worse
> > > > > > than
> > > > > > it
> > > > > > already is right?
> > > > > >
> > > > > > Before this change we where always calling
> > > > > > FLUSH_VERTICES(ctx,
> > > > > > _NEW_PROGRAM);
> > > > >
> > > > > The useless flagging is a different issue.
> > > > >
> > > > > FLUSH_VERTICES should be called before a state change,
> > > > > because it
> > > > > flushes draw calls that the driver hasn't even seen yet.
> > > > > After
> > > > > the
> > > > > driver processes those draw calls, _NEW_PROGRAM is set.
> > > > > That's
> > > > > how it
> > > > > works.
> > > > >
> > > > > If you instead change a state and then call FLUSH_VERTICES,
> > > > > the
> > > > > previous unflushed draw calls will use the new state, which
> > > > > is
> > > > > incorrect.
> > > >
> > > > But the state doesn't change just from linking does it? The new
> > > > programs won't be made current until glUseProgram() is called.
> > >
> > > The GL state changes if the program is current and re-linked.
> > > (not
> > > sure if all of the internal Mesa state changes too)
> >
> > Right but this patch only changes things so that FLUSH_VERTICES is
> > not
> > called when the program is *not* current.
>
> That idea is OK. The problem is the patch also moves FLUSH_VERTICES
> after the _mesa_glsl_link_shader call, which breaks the behavior if
> the program *is* current.
>
> Consider this:
>
> glUseProgram();
> glBegin();
> glVertex();
> glEnd();
> // the vbo module doesn't create a draw call in glEnd; instead, it
> waits
> // for another glBegin call and the driver doesn't see any draw calls
> yet.
> glDetachShader();
> glAttachShader();
> glLinkProgram() {
> _mesa_glsl_link_shader(); // this replaces the current program
> FLUSH_VERTICES(); // this finally creates the draw call from
> Begin/End,
> // but with the new program
> }
>
>
> The correct sequence is:
>
> glLinkProgram() {
> FLUSH_VERTICES(); // create the draw call from Begin/End
> _mesa_glsl_link_shader(); // replace the current program
> }
ok I've taken a closer look at things and see what you getting at. My
reason for moving it later is to prepare for patch 34 [1].
I guess I could do:
if (shProg->data->LinkStatus && programs_in_use) {
FLUSH_VERTICES(ctx, 0);
FLUSH_VERTICES(ctx, _NEW_PROGRAM);
}
Which will later become:
if (shProg->data->LinkStatus && programs_in_use) {
FLUSH_VERTICES(ctx, 0);
while (programs_in_use) {
const int stage = u_bit_scan(&programs_in_use);
struct gl_program *prog = NULL;
if (shProg->_LinkedShaders[stage])
prog = shProg->_LinkedShaders[stage]->Program;
_mesa_use_program(ctx, stage, prog, ctx->_Shader);
}
}
[1] https://lists.freedesktop.org/archives/mesa-dev/2017-January/139351
.html
>
> Marek
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