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PR30724, cygwin ld performance regression since 014a602b86

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According to the reporter of this bug the newlib fseek implementation
is likely slowed down by locking and fflush, only attempting to
optimise seeks when the file is opened read-only.  Thus when writing
the output we get a dramatic slowdown due to commit 014a602b86.

	PR 30724
	* bfd.c (enum bfd_last_io): New.
	(struct bfd): Add last_io field.
	* bfd-in2.h: Regenerate.
	* bfd-io.c (bfd_bread, bfd_bwrite): Force seek if last_io is
	opposite direction.
	(bfd_seek): Reinstate optimisation for seek to same position.
This commit is contained in:
Alan Modra 2023-08-07 08:28:55 +09:30
parent 7570a17cbb
commit f82ee0c8dc
3 changed files with 67 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
bfd/bfd-in2.h
View File

@ -1916,6 +1916,14 @@ enum bfd_direction
both_direction = 3
};
enum bfd_last_io
{
bfd_io_seek = 0,
bfd_io_read = 1,
bfd_io_write = 2,
bfd_io_force = 3
};
enum bfd_plugin_format
{
bfd_plugin_unknown = 0,
@ -2068,6 +2076,20 @@ struct bfd
/* The direction with which the BFD was opened. */
ENUM_BITFIELD (bfd_direction) direction : 2;
/* POSIX.1-2017 (IEEE Std 1003.1) says of fopen : "When a file is
opened with update mode ('+' as the second or third character in
the mode argument), both input and output may be performed on
the associated stream. However, the application shall ensure
that output is not directly followed by input without an
intervening call to fflush() or to a file positioning function
(fseek(), fsetpos(), or rewind()), and input is not directly
followed by output without an intervening call to a file
positioning function, unless the input operation encounters
end-of-file."
This field tracks the last IO operation, so that bfd can insert
a seek when IO direction changes. */
ENUM_BITFIELD (bfd_last_io) last_io : 2;
/* Is the file descriptor being cached? That is, can it be closed as
needed, and re-opened when accessed later? */
unsigned int cacheable : 1;

22
bfd/bfd.c
View File

@ -53,6 +53,14 @@ EXTERNAL
. both_direction = 3
. };
.
.enum bfd_last_io
. {
. bfd_io_seek = 0,
. bfd_io_read = 1,
. bfd_io_write = 2,
. bfd_io_force = 3
. };
.
.enum bfd_plugin_format
. {
. bfd_plugin_unknown = 0,
@ -208,6 +216,20 @@ CODE_FRAGMENT
. {* The direction with which the BFD was opened. *}
. ENUM_BITFIELD (bfd_direction) direction : 2;
.
. {* POSIX.1-2017 (IEEE Std 1003.1) says of fopen : "When a file is
. opened with update mode ('+' as the second or third character in
. the mode argument), both input and output may be performed on
. the associated stream. However, the application shall ensure
. that output is not directly followed by input without an
. intervening call to fflush() or to a file positioning function
. (fseek(), fsetpos(), or rewind()), and input is not directly
. followed by output without an intervening call to a file
. positioning function, unless the input operation encounters
. end-of-file."
. This field tracks the last IO operation, so that bfd can insert
. a seek when IO direction changes. *}
. ENUM_BITFIELD (bfd_last_io) last_io : 2;
.
. {* Is the file descriptor being cached? That is, can it be closed as
. needed, and re-opened when accessed later? *}
. unsigned int cacheable : 1;

23
bfd/bfdio.c
View File

@ -279,6 +279,14 @@ bfd_bread (void *ptr, bfd_size_type size, bfd *abfd)
return -1;
}
if (abfd->last_io == bfd_io_write)
{
abfd->last_io = bfd_io_force;
if (bfd_seek (abfd, 0, SEEK_CUR) != 0)
return -1;
}
abfd->last_io = bfd_io_read;
nread = abfd->iovec->bread (abfd, ptr, size);
if (nread != -1)
abfd->where += nread;
@ -313,6 +321,14 @@ bfd_bwrite (const void *ptr, bfd_size_type size, bfd *abfd)
return -1;
}
if (abfd->last_io == bfd_io_read)
{
abfd->last_io = bfd_io_force;
if (bfd_seek (abfd, 0, SEEK_CUR) != 0)
return -1;
}
abfd->last_io = bfd_io_write;
nwrote = abfd->iovec->bwrite (abfd, ptr, size);
if (nwrote != -1)
abfd->where += nwrote;
@ -456,6 +472,13 @@ bfd_seek (bfd *abfd, file_ptr position, int direction)
if (direction != SEEK_CUR)
position += offset;
if (((direction == SEEK_CUR && position == 0)
|| (direction == SEEK_SET && (ufile_ptr) position == abfd->where))
&& abfd->last_io != bfd_io_force)
return 0;
abfd->last_io = bfd_io_seek;
result = abfd->iovec->bseek (abfd, position, direction);
if (result != 0)
{