This is the mail archive of the
gdb-patches@sourceware.org
mailing list for the GDB project.
[patch] Minor O_CLOEXEC optimization, "regression" fix
- From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- To: gdb-patches at sourceware dot org
- Date: Tue, 8 Oct 2013 20:32:14 +0200
- Subject: [patch] Minor O_CLOEXEC optimization, "regression" fix
- Authentication-results: sourceware.org; auth=none
Hi Tom,
I just noticed GDB does many needless double-opens with ENOENT like:
open("/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY) = -1 ENOENT (No such file or directory)
The fix is simple, it saved 30 syscalls on a small example (3076->3046) like:
open("/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
-open("/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/lib/debug/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
-open("/usr/lib/debug/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/gdb/auto-load/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
-open("/usr/share/gdb/auto-load/usr/lib64/libc-2.18.90.so-gdb.gdb", O_RDONLY) = -1 ENOENT (No such file or directory)
No regressions on {x86_64,x86_64-m32,i686}-fedora21pre-linux-gnu.
Jan
gdb/
2013-10-08 Jan Kratochvil <jan.kratochvil@redhat.com>
Minor performance optimization of opening non-existing files.
* common/filestuff.c (gdb_fopen_cloexec): New variable
fopen_e_ever_succeeded, use it.
diff --git a/gdb/common/filestuff.c b/gdb/common/filestuff.c
index d3b13e8..e10a013 100644
--- a/gdb/common/filestuff.c
+++ b/gdb/common/filestuff.c
@@ -319,6 +319,10 @@ gdb_fopen_cloexec (const char *filename, const char *opentype)
supported. */
static int fopen_e_ever_failed = O_CLOEXEC == 0;
+ /* If we know the operating system supports "e" do not retry the open
+ without "e". The file for example just does not exist. */
+ static int fopen_e_ever_succeeded;
+
if (!fopen_e_ever_failed)
{
char *copy;
@@ -331,7 +335,9 @@ gdb_fopen_cloexec (const char *filename, const char *opentype)
result = fopen (filename, copy);
}
- if (result == NULL)
+ if (result != NULL)
+ fopen_e_ever_succeeded = 1;
+ else if (!fopen_e_ever_succeeded)
{
/* Fallback. */
result = fopen (filename, opentype);