Re: Vim surprisingly slow?

On Mi, 15 Nov 2017, Dominique Pellé wrote:

> As highlighted in red, notice that we only write 179,281 bytes to file
> "20150425.txt" but we open/write/close/fsync 5004 times.
> That repeated I/O patterns kills performance, especially because
> of the frequent fsync().
>
> We also read 1,612,897 bytes from data.json, but that should be
> fast since we do only 27 read and opened that file only twice
> according to output of io.pl. Vim reads file deta.json by chunks
> of 64 KB. 1,612,897 bytes is exactly the file size of data.json.
>
> Maybe we can change vim to avoid the constant open/write/close/fsync
> on file "20150425.txt" which should speed it up greatly.

Thanks for this nice analysis. It is probably the fsync call that is
slowing Vim down. We can avoid the fsync by disabling the 'fsync'
option. Also we might want to disable the writebackup option just in
case it matters. And finally, when a file is written in a different
encoding, Vim will try to check if conversion is safe by first trying to
convert the buffer contents to the fileencoding before writing the file.
That might make also a difference when encoding differs from the file
encoding.

Perhaps it makes sense to skip fsyncing while being busy in a `:g`
command. Tim, does this patch make a difference?

diff --git a/src/fileio.c b/src/fileio.c
index d991822c3..eb626a675 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4731,7 +4731,7 @@ restore_backup:
* work (could be a pipe).
* If the 'fsync' option is FALSE, don't fsync(). Useful for laptops.
*/
- if (p_fs && fsync(fd) != 0 && !device)
+ if (p_fs && !global_busy && fsync(fd) != 0 && !device)
{
errmsg = (char_u *)_("E667: Fsync failed");
end = 0;

Christian
--
Was auch immer, du mich auch.

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