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Improve sparse I/O performance

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* src/sparse.c (sparse_dump_region, sparse_extract_region):
Don’t insist on reading and writing sparse files 512
bytes at a time.  This resulted in a 4× to 6× performance
improvement on my platform.
This commit is contained in:
Paul Eggert
2024-11-02 13:06:47 -07:00
parent c500103600
commit 568919d77b
2 changed files with 12 additions and 6 deletions
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6
NEWS
View File

@@ -1,4 +1,4 @@
GNU tar NEWS - User visible changes. 2023-09-12
GNU tar NEWS - User visible changes. 2024-11-02
Please send GNU tar bug reports to <bug-tar@gnu.org>
version TBD
@@ -36,6 +36,10 @@ used, command output will be parsed using strptime(3).
** Transformations that change case (e.g., --transform='s/.*/\L&/')
now work correctly with multi-byte characters.
* Performance improvements
** Sparse files are now read and written with larger blocksizes.
version 1.35 - Sergey Poznyakoff, 2023-07-18

12
src/sparse.c
View File

@@ -415,7 +415,8 @@ sparse_dump_region (struct tar_sparse_file *file, idx_t i)
while (bytes_left > 0)
{
union block *blk = find_next_block ();
idx_t bufsize = min (bytes_left, BLOCKSIZE);
idx_t avail = available_space_after (blk);
idx_t bufsize = min (bytes_left, avail);
idx_t bytes_read = full_read (file->fd, blk->buffer, bufsize);
if (bytes_read < BLOCKSIZE)
memset (blk->buffer + bytes_read, 0, BLOCKSIZE - bytes_read);
@@ -449,7 +450,7 @@ sparse_dump_region (struct tar_sparse_file *file, idx_t i)
return false;
}
set_next_block_after (blk);
set_next_block_after (blk + (bufsize - 1) / BLOCKSIZE);
}
return true;
@@ -473,15 +474,16 @@ sparse_extract_region (struct tar_sparse_file *file, idx_t i)
}
else while (write_size > 0)
{
idx_t wrbytes = min (write_size, BLOCKSIZE);
union block *blk = find_next_block ();
if (!blk)
{
paxerror (0, _("Unexpected EOF in archive"));
return false;
}
set_next_block_after (blk);
file->dumped_size += BLOCKSIZE;
idx_t avail = available_space_after (blk);
idx_t wrbytes = min (write_size, avail);
set_next_block_after (blk + (wrbytes - 1) / BLOCKSIZE);
file->dumped_size += avail;
idx_t count = blocking_write (file->fd, blk->buffer, wrbytes);
write_size -= count;
mv_size_left (file->stat_info->archive_file_size - file->dumped_size);