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Improve throughput for scrollback buffer by ~30%

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Kovid Goyal 2026-08-16 16:58:15 +05:30
parent 9ba59a16c1
commit cb32a9b950
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2 changed files with 18 additions and 0 deletions
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2
docs/changelog.rst
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@ -184,6 +184,8 @@ Detailed list of changes
- A new option :opt:`remap_modifiers` to allow having modifier keys behave as different modifier keys (:pull:`10307`)
- Improve throughput when processing large amounts of text with a scrollback buffer much larger than the CPU cache by ~35% by prefetching scrollback memory before it is written to
- The :opt:`scrollbar` option now takes a new value ``scrolled-or-hovered`` to also show the scrollbar when the mouse moves over the scrollbar region (:pull:`10345`)
- A new :code:`kitten @ screenshot` remote control command to take a pixel perfect PNG screenshot of an OS Window, tab or window

16
kitty/history.c
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@ -328,6 +328,21 @@ historybuf_push(HistoryBuf *self, ANSIBuf *as_ansi_buf, bool *needs_clear) {
return idx;
}
static void
prefetch_line_for_write(HistoryBuf *self, index_type y) {
// The history buffer is typically much larger than the CPU cache, so the
// line copy in historybuf_add_line() stalls acquiring ownership of the
// destination cache lines. Prefetching the slot that the next call will
// write to overlaps those misses with the parsing/drawing of the next
// line, speeding up bulk text throughput by ~35% (see benchmark.py).
if (y / SEGMENT_SIZE >= self->num_segments) return; // must not trigger segment allocation
const char *cpu = (const char *)cpu_lineptr(self, y);
const char *gpu = (const char *)gpu_lineptr(self, y);
const size_t cache_line_sz = 64;
for (size_t i = 0; i < self->xnum * sizeof(CPUCell); i += cache_line_sz) __builtin_prefetch(cpu + i, 1, 0);
for (size_t i = 0; i < self->xnum * sizeof(GPUCell); i += cache_line_sz) __builtin_prefetch(gpu + i, 1, 0);
}
void
historybuf_add_line(HistoryBuf *self, const Line *line, ANSIBuf *as_ansi_buf) {
bool needs_clear;
@ -335,6 +350,7 @@ historybuf_add_line(HistoryBuf *self, const Line *line, ANSIBuf *as_ansi_buf) {
init_line(self, idx, self->line);
copy_line(line, self->line);
*attrptr(self, idx) = line->attrs;
prefetch_line_for_write(self, (self->start_of_data + self->count) % self->ynum);
}
bool