bug#27097: Combining Guix, direnv and Emacs for environment customisation

[ludo@gnu.org (Ludovic Courtès)]

Roel Janssen <roel@gnu.org> skribis:

> Ludovic Courtès writes:
>
>> I agree that we could do a lot more things with a faster ‘guix
>> environment’.  My guess is that it won’t be easy to go optimize, and
>> very hard to go below 1 second.  We should profile that and see what can
>> be done.
>
> FWIW, on our NFS-mounted /gnu, the 'guix environment' command takes at
> least 20 seconds, but for any reasonably big environment it takes more
> than one minute.  The biggest bottleneck here is the disk latency.
> Could it be that 'guix environment' accesses many files?  If we could
> reduce that, it would speed things up (at least for us ;)).

Interesting.   Does guix-daemon access /gnu over NFS too?

Could you send the output of (first run the same command without
‘strace’):

  strace -c guix environment --ad-hoc coreutils --pure -- true

On my laptop I get:

--8<---------------cut here---------------start------------->8---
$ strace -c guix environment --ad-hoc coreutils --pure -- true
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 37.84    0.017268           1     14036     10965 stat
 15.13    0.006904           1      9990           read
 14.02    0.006398           1     10000           write
  8.75    0.003991        3991         1           wait4
  6.06    0.002764           1      5218         4 lstat
  4.73    0.002157           1      1930       136 open
  2.58    0.001176           1      1794           close
  2.08    0.000949           1      1717         3 lseek
  2.04    0.000932           1       689           mmap
  1.89    0.000861           1       645           mprotect
  1.71    0.000781           4       189        32 futex

[…]
--8<---------------cut here---------------end--------------->8---

We stat a lot mostly to access all the Guix modules.  Are they on NFS
too?

Thanks,
Ludo’.