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commit 2e0458f23b0a25771ab7e6fd77d7068ad1d7fa38
Author: [email protected] <[email protected]>
AuthorDate: Mon Apr 6 15:00:23 2026 -0600
perf(evas_ector_gl): move sentinel writes to collection phase for cache locality
The span-buffer pipeline previously wrote zero-length sentinels during GPU upload
(span_collector_upload_textures), when the buffer was cold and scattered across
memory. This incurred repeated L3-cache misses across 50+ texture rows.
Move sentinel writes to two hot-cache locations:
1. _collect_spans_solid: Track row transitions (prev_y, prev_ti). When y changes,
the previous row is complete in L1-D cache. Memset the tail (from the last
written span entry to max_spans+1) in one operation. This writes the len=0
sentinel implicitly AND clears stale data from prior frames, all while the
buffer is hot.
2. span_collector_clear: For rows that receive no spans this frame, zero byte[1]
(the len field) of entry 0 on all rows. Rows with zero spans never get a row-
change memset, so the shader must find a valid sentinel at entry 0.
3. _do_spatial_split: Add tail memsets after redistribution. Splits happen mid-
collection, so entries beyond the new span_counts may retain stale len bytes
from the pre-split data. Memset both old and new texture tails.
Remove the sentinel write loop from span_collector_upload_textures entirely. The
invariant is now maintained during collection (when hot) and clear (once per frame).
Performance impact: Reduces cache misses on texture row iteration (~50 L3 hits
become L1 hits or single L2 sweep), amortized ~1-2 cycles per row during upload.
Add two unit tests:
- span_collector_solid_tail_memset: Verify full tail is zeroed after collection
- span_collector_clear_stale_sentinel: Verify stale rows have valid len=0 sentinel
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
---
.../evas/engines/gl_generic/evas_ector_gl_span.c | 96 ++++++++++++++++++----
.../engines/gl_generic/evas_ector_gl_span_shader.c | 30 ++-----
src/tests/ector/suite/ector_test_span_collector.c | 96 ++++++++++++++++++++++
3 files changed, 187 insertions(+), 35 deletions(-)
diff --git a/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c b/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c
index 6a98bc74f4..8ee56ecee4 100644
--- a/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c
+++ b/src/modules/evas/engines/gl_generic/evas_ector_gl_span.c
@@ -228,17 +228,32 @@ span_collector_clear(Span_Collector *sc)
/* Only zero sc->height rows (the active region), not alloc_height.
* This is safe because:
* - span_collector_resize zeros newly added rows when growing
- * - span_counts[y] = 0 causes the shader to hit the len=0 sentinel
- * at entry index 0, so stale buffer data beyond entry 0 is never read
+ * - _collect_spans_solid memsets the tail of each row (from the last
+ * written entry to max_spans+1) during collection, which writes the
+ * sentinel implicitly for rows that receive spans
+ * - for rows that receive NO spans this frame, we zero byte[1] of entry 0
+ * here so the shader sees len=0 and stops immediately (the rest of the
+ * buffer may retain stale data, but the shader never reaches it)
* - clear is always called after resize, which has already set height */
{
int i;
for (i = 0; i < sc->texture_count; i++)
{
- memset(sc->textures[i].span_counts, 0, sc->height * sizeof(int));
- memset(sc->textures[i].last_x_end, 0, sc->height * sizeof(int));
- sc->textures[i].dirty = EINA_FALSE;
- sc->textures[i].rolling_hash = 2166136261u; /* seed */
+ Span_Texture *tex = &sc->textures[i];
+ int y;
+
+ memset(tex->span_counts, 0, sc->height * sizeof(int));
+ memset(tex->last_x_end, 0, sc->height * sizeof(int));
+
+ /* Zero byte[1] (len) of entry 0 on every row so that rows
+ * which receive no spans this frame have a valid sentinel.
+ * _collect_spans_solid memsets the full tail for rows it touches,
+ * so this 4-byte-stride write covers only the uncollected rows. */
+ for (y = 0; y < sc->height; y++)
+ tex->buffer[(size_t)y * sc->stride + 1] = 0; /* byte[1] = len = 0 */
+
+ tex->dirty = EINA_FALSE;
+ tex->rolling_hash = 2166136261u; /* seed */
}
}
@@ -564,6 +579,17 @@ _do_spatial_split(Span_Collector *sc, int overflow_y)
old_tex->last_x_end[y] = left_last;
new_tex->span_counts[y] = right_idx;
new_tex->last_x_end[y] = right_last;
+
+ /* Clear tails of redistributed rows — stale entries beyond the
+ * new span_counts have non-zero len bytes from the pre-split data.
+ * The collection callback's row-change memset won't cover these
+ * since the split happens mid-collection. */
+ if (left_idx < sc->max_spans)
+ memset(left_row + (size_t)left_idx * 4, 0,
+ (size_t)(sc->max_spans + 1 - left_idx) * 4);
+ if (right_idx < sc->max_spans)
+ memset(right_row + (size_t)right_idx * 4, 0,
+ (size_t)(sc->max_spans + 1 - right_idx) * 4);
}
/* Mark both textures dirty so the next upload path recreates them. */
@@ -616,7 +642,13 @@ _find_texture_for_x(Span_Collector *sc, int x)
* byte 3: reserved (zero)
*
* The base color is passed to the shader as a uniform, not per-span.
- * A zero-length sentinel (byte[1] = 0) terminates the row.
+ * A zero-length sentinel (byte[1] = 0) terminates the row; it is written
+ * implicitly by memset-ing the tail of the row (from span_counts[y] to
+ * max_spans+1) once per row when y changes. The buffer is hot in L1-D
+ * from the span writes, so the memset is nearly free.
+ *
+ * Rows that receive no spans have their sentinel guaranteed by
+ * span_collector_clear, which zeroes byte[1] of entry 0 on all rows.
*
* Spans with y outside [0, height) are silently skipped.
* When a row hits max_spans, a spatial split is attempted (_do_spatial_split).
@@ -630,6 +662,8 @@ _collect_spans_solid(int count, const SW_FT_Span *spans, void *user_data)
Span_Data *sd = (Span_Data *)user_data;
Span_Collector *sc = (Span_Collector *)sd->span_collector;
int ti, idx, y, sx;
+ int prev_y = -1;
+ int prev_ti = -1;
Span_Texture *tex;
uint8_t *entry;
@@ -657,6 +691,29 @@ _collect_spans_solid(int count, const SW_FT_Span *spans, void *user_data)
continue;
}
+ /* FreeType delivers spans in row order (y non-decreasing within a
+ * callback). When y changes, the previous row is complete: memset
+ * the tail from the last written entry to the end of the row.
+ *
+ * This writes the zero-length sentinel implicitly (entry at
+ * span_counts[prev_y] has len=0 after zeroing) AND clears any stale
+ * data from prior frames beyond the current frame's last span.
+ * The buffer is hot in L1-D from the span writes above, so the
+ * memset is nearly free.
+ *
+ * Only fires when y actually changes — not once per span. */
+ if (y != prev_y && prev_y >= 0 && prev_ti >= 0)
+ {
+ Span_Texture *prev_tex = &sc->textures[prev_ti];
+ int prev_idx = prev_tex->span_counts[prev_y];
+
+ if (prev_idx < sc->max_spans)
+ memset(prev_tex->buffer +
+ ((size_t)prev_y * sc->stride) + ((size_t)prev_idx * 4),
+ 0,
+ (size_t)(sc->max_spans + 1 - prev_idx) * 4);
+ }
+
ti = (sc->texture_count == 1) ? 0 : _find_texture_for_x(sc, sx);
tex = &sc->textures[ti];
idx = tex->span_counts[y];
@@ -744,17 +801,28 @@ _collect_spans_solid(int count, const SW_FT_Span *spans, void *user_data)
if (idx > sc->actual_max_spans)
sc->actual_max_spans = idx;
- /* Write zero-length sentinel after the last entry on this row. */
- if (idx < sc->max_spans)
- {
- uint8_t *sentinel = tex->buffer +
- ((size_t)y * sc->stride) + ((size_t)idx * 4);
- sentinel[1] = 0; /* len = 0 marks end of row */
- }
+ prev_y = y;
+ prev_ti = ti;
spans++;
count--;
}
+
+ /* Memset the tail of the last row after the loop ends.
+ * The row-change path above fires only when y changes, so the final
+ * row (or the only row when the shape spans a single scanline) is
+ * handled here. */
+ if (prev_y >= 0 && prev_ti >= 0)
+ {
+ Span_Texture *prev_tex = &sc->textures[prev_ti];
+ int prev_idx = prev_tex->span_counts[prev_y];
+
+ if (prev_idx < sc->max_spans)
+ memset(prev_tex->buffer +
+ ((size_t)prev_y * sc->stride) + ((size_t)prev_idx * 4),
+ 0,
+ (size_t)(sc->max_spans + 1 - prev_idx) * 4);
+ }
}
/* ------------------------------------------------------------------ */
diff --git a/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c b/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c
index 2e1a74cd49..95d1e28ad8 100644
--- a/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c
+++ b/src/modules/evas/engines/gl_generic/evas_ector_gl_span_shader.c
@@ -850,7 +850,6 @@ span_collector_upload_textures(Span_Collector *sc, void *gc_ptr)
{
Span_Texture *tex = &sc->textures[i];
Evas_GL_Texture *evas_t;
- int y;
/* Recreate the GPU texture if the active height changed
* (the sub-region within the pool was allocated for a different height). */
@@ -884,27 +883,16 @@ span_collector_upload_textures(Span_Collector *sc, void *gc_ptr)
}
}
- /* Write sentinels for rows that have spans.
+ /* Sentinel write is no longer needed here.
*
- * All fill types (Solid and gradient) use 1-texel-per-span BGRA layout:
- * byte[1] holds len (the G channel). Setting byte[1] = 0 writes a
- * zero-length sentinel that terminates the shader's span scan loop. */
- for (y = 0; y < sc->height; y++)
- {
- int idx = tex->span_counts[y];
- /* Do NOT skip idx==0 rows — the buffer is not zeroed by
- * span_collector_clear, so stale span data from previous
- * frames may have len != 0. The sentinel write at entry 0
- * ensures the shader sees len=0 and stops immediately. */
- if (idx < sc->max_spans)
- {
- int bps = 4;
- uint8_t *sentinel = tex->buffer +
- ((size_t)y * sc->stride) +
- ((size_t)idx * bps);
- sentinel[1] = 0; /* byte[1] = len (BGRA G channel) = 0 */
- }
- }
+ * _collect_spans_solid memsets the full tail of each row it touches
+ * (from span_counts[y] to max_spans+1) during collection, which
+ * implicitly writes the len=0 sentinel AND clears stale data from
+ * previous frames in a single L1-hot memset.
+ *
+ * For rows that receive NO spans this frame, span_collector_clear
+ * zeroes byte[1] (len) of entry 0 on every row, so the shader
+ * sees len=0 at the very first entry and terminates immediately. */
/* First frame: create the Evas texture via the standard path.
* Subsequent dirty frames: update in-place via glTexSubImage2D.
diff --git a/src/tests/ector/suite/ector_test_span_collector.c b/src/tests/ector/suite/ector_test_span_collector.c
index d812ab571f..bfb8c446da 100644
--- a/src/tests/ector/suite/ector_test_span_collector.c
+++ b/src/tests/ector/suite/ector_test_span_collector.c
@@ -698,6 +698,100 @@ EFL_START_TEST(span_collector_solid_overflow_drop)
}
EFL_END_TEST
+/* ------------------------------------------------------------------ */
+/* Test: tail memset zeroes the full tail of a row, not just byte[1] */
+/* ------------------------------------------------------------------ */
+
+/*
+ * Write one span, then verify that ALL bytes from the entry after
+ * span_counts[y] to the end of the row (including the sentinel slot)
+ * are zero. This confirms the memset covers the full tail rather than
+ * writing only a single sentinel byte.
+ */
+EFL_START_TEST(span_collector_solid_tail_memset)
+{
+ Span_Collector *sc;
+ Span_Data sd;
+ SW_FT_Span span;
+ uint8_t *row;
+ int tail_start, tail_bytes, b;
+
+ sc = span_collector_new(50, 16, Solid);
+ ck_assert_ptr_nonnull(sc);
+
+ /* Pollute the buffer with non-zero bytes to simulate stale data. */
+ memset(sc->textures[0].buffer, 0xAB, (size_t)50 * sc->stride);
+
+ _sd_init_solid(&sd, sc, 0xFFFFFFFF);
+
+ span.x = 10;
+ span.y = 7;
+ span.len = 20;
+ span.coverage = 200;
+ _collect_spans_solid(1, &span, &sd);
+
+ ck_assert_int_eq(sc->textures[0].span_counts[7], 1);
+
+ /* Tail starts at entry 1 (one past the span) and runs to max_spans+1. */
+ row = sc->textures[0].buffer + (7 * sc->stride);
+ tail_start = 1 * 4; /* first tail entry */
+ tail_bytes = (sc->max_spans + 1 - 1) * 4; /* sentinel slot included */
+
+ for (b = 0; b < tail_bytes; b++)
+ ck_assert_int_eq(row[tail_start + b], 0);
+
+ span_collector_free(sc);
+}
+EFL_END_TEST
+
+/* ------------------------------------------------------------------ */
+/* Test: clear zeroes byte[1] of entry 0 so stale rows have sentinel */
+/* ------------------------------------------------------------------ */
+
+/*
+ * Frame 1: write a span on row 3, leaving non-zero data in the buffer.
+ * Call span_collector_clear (simulating a frame boundary).
+ * Frame 2: write NO span on row 3.
+ *
+ * Verify that byte[1] of entry 0 on row 3 is 0 after clear — the shader
+ * must see len=0 at the very first entry on a row that received no spans.
+ */
+EFL_START_TEST(span_collector_clear_stale_sentinel)
+{
+ Span_Collector *sc;
+ Span_Data sd;
+ SW_FT_Span span;
+ uint8_t *entry0;
+
+ sc = span_collector_new(20, 8, Solid);
+ ck_assert_ptr_nonnull(sc);
+
+ _sd_init_solid(&sd, sc, 0xFFFF0000);
+
+ /* Frame 1: write a span on row 3. */
+ span.x = 5;
+ span.y = 3;
+ span.len = 30;
+ span.coverage = 255;
+ _collect_spans_solid(1, &span, &sd);
+
+ ck_assert_int_eq(sc->textures[0].span_counts[3], 1);
+
+ /* Simulate frame boundary. */
+ span_collector_resize(sc, 20);
+ span_collector_clear(sc);
+
+ /* Frame 2: no spans written on row 3. span_counts[3] == 0. */
+ ck_assert_int_eq(sc->textures[0].span_counts[3], 0);
+
+ /* byte[1] of entry 0 must be 0 — the sentinel the shader relies on. */
+ entry0 = sc->textures[0].buffer + (3 * sc->stride);
+ ck_assert_int_eq(entry0[1], 0);
+
+ span_collector_free(sc);
+}
+EFL_END_TEST
+
/* ------------------------------------------------------------------ */
/* Registration */
/* ------------------------------------------------------------------ */
@@ -715,4 +809,6 @@ ector_test_span_collector(TCase *tc)
tcase_add_test(tc, span_collector_post_split_routing);
tcase_add_test(tc, span_collector_gradient_basic);
tcase_add_test(tc, span_collector_solid_overflow_drop);
+ tcase_add_test(tc, span_collector_solid_tail_memset);
+ tcase_add_test(tc, span_collector_clear_stale_sentinel);
}
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