Re: Vim surprisingly slow?

Christian Brabandt <cblists@256bit.org> wrote:

> 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;


Hi Christian

I measured the same command twice before and after your patch:

Before patch:

$ time ./vim -u NONE data.json -S new_engine.vim
real 0m15.533s
user 0m1.648s
sys 0m0.824s

$ time ./vim -u NONE data.json -S new_engine.vim

real 0m15.444s
user 0m1.636s
sys 0m0.820s

After patch:

$ time ./vim -u NONE data.json -S new_engine.vim

real 0m0.741s
user 0m0.536s
sys 0m0.200s

$ time ./vim -u NONE data.json -S new_engine.vim

real 0m0.731s
user 0m0.548s
sys 0m0.184s

So your patch makes it more than 20 times faster
on my Linux machine. Nice! Hopefully it's safe to
avoid fsync() in this case.

Regards
Dominique

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