Optimize tty display updates (bug#57727)

* src/dispnew.c (update_frame_1): Don'f flush if tty's
output_buffer_size is non-zero.
* src/sysdep.c (init_sys_modes): Setvbuf depending on the tty's
output_buffer_size.
* src/term.c (Ftty__set_output_buffer_size, Ftty__output_buffer_size):
Low-level interface for setting and retrieving a tty's output buffer
size.
(syms_of_term): Defsubr the new functions.
* src/termchar.h (struct tty_display_info): New member
output_buffer_size.
* stc/NEWS: Describe the change.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/sysdep.c b/src/sysdep.c
index efd9638b07a..abb385d1388 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -1304,7 +1304,10 @@ init_sys_modes (struct tty_display_info *tty_out)
     }
 #endif /* F_GETOWN */
 
-  setvbuf (tty_out->output, NULL, _IOFBF, BUFSIZ);
+  const size_t buffer_size = (tty_out->output_buffer_size
+                              ? tty_out->output_buffer_size
+                              : BUFSIZ);
+  setvbuf (tty_out->output, NULL, _IOFBF, buffer_size);
 
   if (tty_out->terminal->set_terminal_modes_hook)
     tty_out->terminal->set_terminal_modes_hook (tty_out->terminal);