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scrolling: optimize row access by assuming number of rows is a power of 2

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With this assumption, we can replace 'a % b' with 'a & (b - 1)'. In
terms of instructions, this means a fast 'and' instead of a slow
'div'.

Further optimize scrolling by:

* not double-initializing empty rows. Previously, grid_row_alloc()
  called calloc(), which was then followed by a memset() when
  scrolling. This is of course unnecessary.

* Don't loop the entire set of visible rows (this was done to ensure
  all visible rows had been allocated, and to prefetch the cell
  contents).

  This isn't necessary; only newly pulled in rows can be NULL. For
  now, don't prefetch at all.
This commit is contained in:
Daniel Eklöf 2019-08-22 17:33:23 +02:00
parent f0663c951e
commit 7c7720a3ab
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GPG key ID: 5BBD4992C116573F
5 changed files with 107 additions and 56 deletions
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63
terminal.c
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@ -254,36 +254,47 @@ term_scroll_partial(struct terminal *term, struct scroll_region region, int rows
LOG_DBG("scroll: rows=%d, region.start=%d, region.end=%d",
rows, region.start, region.end);
assert(rows < term->rows && "unimplemented");
#if 0
if (rows > region.end - region.start) {
/* For now, clamp */
rows = region.end - region.start;
}
#endif
bool view_follows = term->grid->view == term->grid->offset;
term->grid->offset += rows;
term->grid->offset %= term->grid->num_rows;
term->grid->offset &= term->grid->num_rows - 1;
if (view_follows)
term->grid->view = term->grid->offset;
#if 0
/*
* This loop serves two purposes:
* 1) ensure all visible lines are *allocated*
* 2) prefetch the cells - this makes life easier for erase_line() below
*/
/* TODO: optimize this to not loop over *all* rows */
for (int r = max(region.end - rows, 0); r < term->rows; r++) {
struct row *row __attribute__((unused)) = grid_row(term->grid, r);
//__builtin_prefetch(row->cells, 1, 3);
int real_row = (term->grid->offset + r) & (term->grid->num_rows - 1);
struct row *row = term->grid->rows[real_row];
if (row == NULL) {
row = grid_row_alloc(term->grid->num_cols, false);
term->grid->rows[real_row] = row;
}
}
#endif
/* Top non-scrolling region. */
for (int i = region.start - 1; i >= 0; i--)
grid_swap_row(term->grid, i - rows, i);
grid_swap_row(term->grid, i - rows, i, false);
/* Bottom non-scrolling region */
for (int i = term->rows - 1; i >= region.end; i--)
grid_swap_row(term->grid, i - rows, i);
grid_swap_row(term->grid, i - rows, i, false);
/* Erase scrolled in lines */
for (int r = max(region.end - rows, 0); r < region.end; r++) {
erase_line(term, grid_row(term->grid, r));
for (int r = max(region.end - rows, region.start); r < region.end; r++) {
erase_line(term, grid_row_and_alloc(term->grid, r));
if (selection_on_row_in_view(term, r))
selection_cancel(term);
}
@ -305,31 +316,47 @@ term_scroll_reverse_partial(struct terminal *term,
LOG_DBG("scroll reverse: rows=%d, region.start=%d, region.end=%d",
rows, region.start, region.end);
assert(rows < term->rows && "unimplemented");
#if 0
if (rows > region.end - region.start) {
/* For now, clamp */
rows = region.end - region.start;
}
#endif
bool view_follows = term->grid->view == term->grid->offset;
term->grid->offset += term->grid->num_rows - rows;
term->grid->offset %= term->grid->num_rows;
term->grid->offset -= rows;
while (term->grid->offset < 0)
term->grid->offset += term->grid->num_rows;
term->grid->offset &= term->grid->num_rows - 1;
assert(term->grid->offset >= 0);
assert(term->grid->offset < term->grid->num_rows);
if (view_follows)
term->grid->view = term->grid->offset;
#if 0
/* TODO: optimize this to not loop over *all* rows */
for (int r = 0; r < min(region.start + rows, region.end); r++) {
struct row *row __attribute__((unused)) = grid_row(term->grid, r);
//__builtin_prefetch(row->cells, 1, 3);
int real_row = (term->grid->offset + r) & (term->grid->num_rows - 1);
struct row *row = term->grid->rows[real_row];
if (row == NULL) {
row = grid_row_alloc(term->grid->num_cols, false);
term->grid->rows[real_row] = row;
}
}
#endif
/* Bottom non-scrolling region */
for (int i = region.end + rows; i < term->rows + rows; i++)
grid_swap_row(term->grid, i, i - rows);
grid_swap_row(term->grid, i, i - rows, false);
/* Top non-scrolling region */
for (int i = 0 + rows; i < region.start + rows; i++)
grid_swap_row(term->grid, i, i - rows);
grid_swap_row(term->grid, i, i - rows, false);
/* Erase scrolled in lines */
for (int r = region.start; r < min(region.start + rows, region.end); r++) {
erase_line(term, grid_row(term->grid, r));
erase_line(term, grid_row_and_alloc(term->grid, r));
if (selection_on_row_in_view(term, r))
selection_cancel(term);
}