[Mesa-dev] [PATCH V2 2/3] mesa: add an env var to force cache fallback

[Timothy Arceri]

For the gallium state tracker a tgsi binary may have been evicted
from the cache to make space. In this case we would take the
fallback path and recompile/link the shader.

On i965 there are a number of reasons we can get to the program
upload stage and have neither IR nor a valid cached binary.
For example the binary may have been evicted from the cache or
we need a variant that wasn't previously cached.

This environment variable enables us to force the fallback path that
would be taken in these cases and makes it easier to debug these
otherwise hard to reproduce scenarios.

V2: drop the infinite loop workaround, it was only required due to
    a bug in the following patch.
---
 docs/shading.html                        | 2 ++
 src/mesa/main/mtypes.h                   | 1 +
 src/mesa/main/shaderapi.c                | 2 ++
 src/mesa/state_tracker/st_shader_cache.c | 6 +++++-
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/docs/shading.html b/docs/shading.html
index 7e3d2e4..c789102 100644
--- a/docs/shading.html
+++ b/docs/shading.html
@@ -43,20 +43,22 @@ Contents
 The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
 list of keywords to control some aspects of the GLSL compiler and shader
 execution.  These are generally used for debugging.
 </p>
 <ul>
 <li><b>dump</b> - print GLSL shader code to stdout at link time
 <li><b>log</b> - log all GLSL shaders to files.
     The filenames will be "shader_X.vert" or "shader_X.frag" where X
     the shader ID.
 <li><b>cache_info</b> - print debug information about shader cache
+<li><b>cache_fb</b> - force cached shaders to be ignored and do a full
+    recompile via the fallback path</li>
 <li><b>uniform</b> - print message to stdout when glUniform is called
 <li><b>nopvert</b> - force vertex shaders to be a simple shader that just transforms
     the vertex position with ftransform() and passes through the color and
     texcoord[0] attributes.
 <li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
     through the color attribute.
 <li><b>useprog</b> - log glUseProgram calls to stderr
 </ul>
 <p>
 Example:  export MESA_GLSL=dump,nopt
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 28d3d948..941311b 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -2970,20 +2970,21 @@ struct gl_shader_program
 
 #define GLSL_DUMP      0x1  /**< Dump shaders to stdout */
 #define GLSL_LOG       0x2  /**< Write shaders to files */
 #define GLSL_UNIFORMS  0x4  /**< Print glUniform calls */
 #define GLSL_NOP_VERT  0x8  /**< Force no-op vertex shaders */
 #define GLSL_NOP_FRAG 0x10  /**< Force no-op fragment shaders */
 #define GLSL_USE_PROG 0x20  /**< Log glUseProgram calls */
 #define GLSL_REPORT_ERRORS 0x40  /**< Print compilation errors */
 #define GLSL_DUMP_ON_ERROR 0x80 /**< Dump shaders to stderr on compile error */
 #define GLSL_CACHE_INFO 0x100 /**< Print debug information about shader cache */
+#define GLSL_CACHE_FALLBACK 0x200 /**< Force shader cache fallback paths */
 
 
 /**
  * Context state for GLSL vertex/fragment shaders.
  * Extended to support pipeline object
  */
 struct gl_pipeline_object
 {
    /** Name of the pipeline object as received from glGenProgramPipelines.
     * It would be 0 for shaders without separate shader objects.
diff --git a/src/mesa/main/shaderapi.c b/src/mesa/main/shaderapi.c
index 68fb3fa..325542e 100644
--- a/src/mesa/main/shaderapi.c
+++ b/src/mesa/main/shaderapi.c
@@ -70,20 +70,22 @@ _mesa_get_shader_flags(void)
    GLbitfield flags = 0x0;
    const char *env = getenv("MESA_GLSL");
 
    if (env) {
       if (strstr(env, "dump_on_error"))
          flags |= GLSL_DUMP_ON_ERROR;
       else if (strstr(env, "dump"))
          flags |= GLSL_DUMP;
       if (strstr(env, "log"))
          flags |= GLSL_LOG;
+      if (strstr(env, "cache_fb"))
+         flags |= GLSL_CACHE_FALLBACK;
       if (strstr(env, "cache_info"))
          flags |= GLSL_CACHE_INFO;
       if (strstr(env, "nopvert"))
          flags |= GLSL_NOP_VERT;
       if (strstr(env, "nopfrag"))
          flags |= GLSL_NOP_FRAG;
       if (strstr(env, "uniform"))
          flags |= GLSL_UNIFORMS;
       if (strstr(env, "useprog"))
          flags |= GLSL_USE_PROG;
diff --git a/src/mesa/state_tracker/st_shader_cache.c b/src/mesa/state_tracker/st_shader_cache.c
index 175d69d..45438e5 100644
--- a/src/mesa/state_tracker/st_shader_cache.c
+++ b/src/mesa/state_tracker/st_shader_cache.c
@@ -218,22 +218,26 @@ st_load_tgsi_from_disk_cache(struct gl_context *ctx,
    }
 
    /* Now that we have created the sha1 keys that will be used for writting to
     * the tgsi cache fallback to the regular glsl to tgsi path if we didn't
     * load the GLSL IR from cache. We do this as glsl to tgsi can alter things
     * such as gl_program_parameter_list which holds things like uniforms.
     */
    if (prog->data->LinkStatus != linking_skipped)
       return false;
 
-   struct st_context *st = st_context(ctx);
    uint8_t *buffer = NULL;
+   if (ctx->_Shader->Flags & GLSL_CACHE_FALLBACK) {
+      goto fallback_recompile;
+   }
+
+   struct st_context *st = st_context(ctx);
    for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
       if (prog->_LinkedShaders[i] == NULL)
          continue;
 
       unsigned char *sha1 = stage_sha1[i];
       size_t size;
       buffer = (uint8_t *) disk_cache_get(ctx->Cache, sha1, &size);
       if (buffer) {
          struct blob_reader blob_reader;
          blob_reader_init(&blob_reader, buffer, size);
-- 
2.9.4