[bug#49421] [PATCH] profiles: Optimise 'fonts-dir-file'.

[Ludovic Courtès]

Hi!

Maxime Devos <maximedevos@telenet.be> skribis:

> Ludovic Courtès schreef op wo 07-07-2021 om 18:52 [+0200]:

[...]

>> Do you know what’s taking time in the ‘fonts-dir-file’ hook?
>> (On my x86_64 laptop with SSD, it runs in 4.4s on a cold cache for a
>> profile containing 14 font packages, and in 1.2s on a warm cache.)
>
> I noticed ‘building fonts directories’ was taking long (9 minutes or so,
> when using "guix package -r two packages that don't have fonts"),

Ouch, that’s way more than what I’m observing.  :-)  Do you have a
manifest or package list to reproduce that?  Were those timings on a
spinning disk?

> so I took the opportunity to "strace" the process, though I was a little late.
> Some statistics:
>
> % time     seconds  usecs/call     calls    errors syscall
> ------ ----------- ----------- --------- --------- ----------------
>  27,14    1,676551         117     14297           rename
>  19,60    1,211012          13     90829         8 lstat
>  18,34    1,133182          63     17787        15 statx
>  11,80    0,729185          51     14297           link

[...]

> statx(AT_FDCWD, "/gnu/store/.links/[...]my", 
> AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, 0, {stx_mask=STATX_ALL|>
> lstat("/gnu/store/.links/[...]my", {st_mode=S_IFLNK|0777, st_size=124, ...}) 
> = 0
> lstat("/gnu/store/[...]nm-fonts-dir/share/fonts/mathjax/HTML-CSS/TeX/png/AMS/Regular/283",
>  {st_mode=S_IFDIR|0555, st_size=4112, ...>
> chmod("/gnu/store/[...]nm-fonts-dir/share/fonts/mathjax/HTML-CSS/TeX/png/AMS/Regular/283",
>  040755) = 0
> getpid()                                = 26371
> <end of log>
>
> It seems like ‘duplication’ is taking a lot of time!

It surely does but we need more data before we can draw a conclusion
(the system time above accounts for ~6 seconds, not 9 minutes).

Anyway, it looks like we should be able to push most of the I/O work to
packages.  Let’s see!

Thanks,
Ludo’.