Re: Time resolution in Emacs

[Max Nikulin]

On 25/04/2022 22:34, Paul Eggert wrote:
> On 4/22/22 23:51, Eli Zaretskii wrote:
>
> > > There are Gnulib library functions to
> > > deal with this sort of thing; it's not a new problem.
> >
> > Doesn't that slow down applications?
>
> Not significantly, no. file-attributes already has the file's filesystem 
> ID and timestamps so Emacs can easily cache that (it's a small cache 
> with only one entry per filesystem). There's no need to traipse through 
> the filesystem looking at other files. This is what coreutils does and 
> it works well in practice. It's not expensive and not that complicated.
>
> Your suggestion of maintaining a static table for known filesystem types 
> is a good one; we could do that to improve common cases. I would like to 
> take a look into doing this.

Notice that on Linux while file metadata are in cache, timestamps may 
have high time resolution. When later fetched from disk they may have 
coarse resolution, e.g. whole seconds.

Generally it is fragile to rely on file modification time. That is why 
build systems relying of file hashes appeared.

As to 16ms resolution, at least for `benchmark-run' I would like to have 
finer granularity.

On the other hand, when higher timer frequency is required, from my 
point of view, it may be better to run such application in a separate 
process.