From: Dmitry Antipov <dmitry.antipov@mail.ru>
Subject: Simple optimization for read_avail_input()
Date: Fri, 30 Jan 2004 18:57:50 +0300 [thread overview]
Message-ID: <401A7EFE.8030509@mail.ru> (raw)
Hello,
this is a top of gprof output for Emacs CVS snapshot. It was being compiled with
'-O0 -ftest-coverage -g -pg -fprofile-arcs', started and finished with C-x C-c
immediately:
Flat profile:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
12.12 0.04 0.04 2464 0.02 0.02 ccl_driver
12.12 0.08 0.04 546 0.07 0.07 read_avail_input
9.09 0.11 0.03 23731 0.00 0.00 read1
9.09 0.14 0.03 4452 0.01 0.01 mark_object
6.06 0.16 0.02 289315 0.00 0.00 readchar
6.06 0.18 0.02 8335 0.00 0.00 Fbyte_code
6.06 0.20 0.02 743 0.03 0.03 Fassoc
3.03 0.21 0.01 136877 0.00 0.00 translate_char
It's clear here that very simple function read_avail_input() wastes a lot of
CPU time. IMHO this is because it wants to zero large 'struct input_event buf'
(which is KBD_BUFFER_SIZE (4096, except old MacOSs) * sizeof (struct input_event)
(44 bytes on 32-bit systems)) every time. But we can clear all 'buf' only once
and clear only used slots next time. The following patch illustrates this idea:
--- keyboard.c.~1.761.~ 2004-01-21 23:19:41.000000000 +0300
+++ keyboard.c 2004-01-30 18:37:04.000000000 +0300
@@ -6568,6 +6568,8 @@
Returns the number of keyboard chars read, or -1 meaning
this is a bad time to try to read input. */
+static int prev_read = KBD_BUFFER_SIZE;
+
static int
read_avail_input (expected)
int expected;
@@ -6576,7 +6578,7 @@
register int i;
int nread;
- for (i = 0; i < KBD_BUFFER_SIZE; i++)
+ for (i = 0; i < prev_read; i++)
EVENT_INIT (buf[i]);
if (read_socket_hook)
@@ -6592,12 +6594,12 @@
/* Determine how many characters we should *try* to read. */
#ifdef WINDOWSNT
- return 0;
+ return (prev_read = 0);
#else /* not WINDOWSNT */
#ifdef MSDOS
n_to_read = dos_keysns ();
if (n_to_read == 0)
- return 0;
+ return (prev_read = 0);
#else /* not MSDOS */
#ifdef FIONREAD
/* Find out how much input is available. */
@@ -6615,7 +6617,7 @@
n_to_read = 0;
}
if (n_to_read == 0)
- return 0;
+ return (prev_read = 0);
if (n_to_read > sizeof cbuf)
n_to_read = sizeof cbuf;
#else /* no FIONREAD */
@@ -6706,7 +6708,7 @@
break;
}
- return nread;
+ return (prev_read = nread);
}
#endif /* not VMS */
Here is an example of gprof output with this patch applied (other conditions
are exactly the same):
Flat profile:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
18.42 0.07 0.07 4453 0.02 0.02 mark_object
10.53 0.11 0.04 36279 0.00 0.00 specbind
7.89 0.14 0.03 2465 0.01 0.01 ccl_driver
5.26 0.16 0.02 8358 0.00 0.01 Fbyte_code
5.26 0.18 0.02 7197 0.00 0.00 re_search_2
2.63 0.19 0.01 289315 0.00 0.00 readchar
2.63 0.20 0.01 156900 0.00 0.00 Faref
...
0.00 0.38 0.00 563 0.00 0.00 call1
0.00 0.38 0.00 548 0.00 0.00 XTread_socket
0.00 0.38 0.00 548 0.00 0.00 read_avail_input
0.00 0.38 0.00 544 0.00 0.00 handle_async_input
So, after several runs, read_avail_input() goes from 1st or 2nd to > 200th
(238 here) place (by CPU usage).
What do you think about this idea ?
Dmitry
next reply other threads:[~2004-01-30 15:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-01-30 15:57 Dmitry Antipov [this message]
2004-02-03 14:17 ` Simple optimization for read_avail_input() Kim F. Storm
2004-02-17 23:51 ` Kim F. Storm
2004-02-20 0:31 ` Kim F. Storm
[not found] <E1Ap8aH-000LqG-00.dmitry-antipov-mail-ru@f7.mail.ru>
2004-02-07 0:12 ` Kim F. Storm
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