[Mesa-dev] [PATCH 08/13] i965: Implement selection of the closest L3 configuration based on a vector of weights.

[Francisco Jerez]

The input of the L3 set-up code is a vector giving the approximate
desired relative size of each partition.  This implements logic to
compare the input vector against the table of validated configurations
for the device and pick the closest compatible one.
---
 src/mesa/drivers/dri/i965/gen7_l3_state.c | 95 +++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/gen7_l3_state.c b/src/mesa/drivers/dri/i965/gen7_l3_state.c
index c863b7f..4d0cfcd 100644
--- a/src/mesa/drivers/dri/i965/gen7_l3_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_l3_state.c
@@ -163,6 +163,101 @@ get_l3_way_size(const struct brw_device_info *devinfo)
 }
 
 /**
+ * L3 configuration represented as a vector of weights giving the desired
+ * relative size of each partition.  The scale is arbitrary, only the ratios
+ * between weights will have an influence on the selection of the closest L3
+ * configuration.
+ */
+struct brw_l3_weights {
+   float w[NUM_L3P];
+};
+
+/**
+ * L1-normalize a vector of L3 partition weights.
+ */
+static struct brw_l3_weights
+norm_l3_weights(struct brw_l3_weights w)
+{
+   float sz = 0;
+
+   for (unsigned i = 0; i < NUM_L3P; i++)
+      sz += w.w[i];
+
+   for (unsigned i = 0; i < NUM_L3P; i++)
+      w.w[i] /= sz;
+
+   return w;
+}
+
+/**
+ * Get the relative partition weights of the specified L3 configuration.
+ */
+static struct brw_l3_weights
+get_config_l3_weights(const struct brw_l3_config *cfg)
+{
+   if (cfg) {
+      struct brw_l3_weights w;
+
+      for (unsigned i = 0; i < NUM_L3P; i++)
+         w.w[i] = cfg->n[i];
+
+      return norm_l3_weights(w);
+   } else {
+      const struct brw_l3_weights w = { { 0 } };
+      return w;
+   }
+}
+
+/**
+ * Distance between two L3 configurations represented as vectors of weights.
+ * Usually just the L1 metric except when the two configurations are
+ * considered incompatible in which case the distance will be infinite.  Note
+ * that the compatibility condition is asymmetric -- They will be considered
+ * incompatible whenever the reference configuration \p w0 requires SLM, DC,
+ * or URB but \p w1 doesn't provide it.
+ */
+static float
+diff_l3_weights(struct brw_l3_weights w0, struct brw_l3_weights w1)
+{
+   if ((w0.w[L3P_SLM] && !w1.w[L3P_SLM]) ||
+       (w0.w[L3P_DC] && !w1.w[L3P_DC] && !w1.w[L3P_ALL]) ||
+       (w0.w[L3P_URB] && !w1.w[L3P_URB])) {
+      return HUGE_VALF;
+
+   } else {
+      float dw = 0;
+
+      for (unsigned i = 0; i < NUM_L3P; i++)
+         dw += fabs(w0.w[i] - w1.w[i]);
+
+      return dw;
+   }
+}
+
+/**
+ * Return the closest validated L3 configuration for the specified device and
+ * weight vector.
+ */
+static const struct brw_l3_config *
+get_l3_config(const struct brw_device_info *devinfo, struct brw_l3_weights w0)
+{
+   const struct brw_l3_config *const cfgs = get_l3_configs(devinfo);
+   const struct brw_l3_config *cfg_best = NULL;
+   float dw_best = HUGE_VALF;
+
+   for (const struct brw_l3_config *cfg = cfgs; cfg->n[L3P_URB]; cfg++) {
+      const float dw = diff_l3_weights(w0, get_config_l3_weights(cfg));
+
+      if (dw < dw_best) {
+         cfg_best = cfg;
+         dw_best = dw;
+      }
+   }
+
+   return cfg_best;
+}
+
+/**
  * Program the hardware to use the specified L3 configuration.
  */
 static void
-- 
2.4.6