Subject: bug#43773: [PATCH] offload: Improve load normalization and configurability.

From: Ludovic Courtès <[email-masked]>
Date: Mon, 05 Oct 2020 16:06:09 +0200

Hi,

Maxim Cournoyer <[email-masked]> skribis:

> Fixes <https://issues.guix.gnu.org/43773>.
>
> The computed normalized load was previously obtained by dividing the load
> average as found in /proc/loadavg by the number of parallel builds defined for
> a build machine.
>
> This normalized didn't allow to compare machines with different number of
                              ^

> cores, as the load average reported by can be as high as the number of cores;
                                        ^
Missing words.

> thus comparing that value to a fixed threshold of 2.0 would mean machines with
> multiple cores were more likely to be flagged as overloaded compared to single
> core machines.
>
> This can be fixed by normalizing using the available number of cores instead
> of the number of parallel jobs.

Indeed, good catch!

> * guix/scripts/offload.scm (<build-machine>)[overload-threshold]: New field.
> (node-load): Modify to return a normalized load value between 0 and 1, taking
> into account the number of cores available.
> (normalized-load): Remove procedure.
> (report-load): New procedure.
> (choose-build-machine): Adjust to use the modified 'node-load' and the new
> 'report-load' and 'build-machine-overload-threshold' procedures.
> (check-machine-status): Adjust.
> * doc/guix.texi (Daemon Offload Setup): Document the offload scheduler and the
> new 'overload-threshold' field.
>
>  doc/guix.texi            | 30 +++++++++++++++++++++-
>  guix/scripts/offload.scm | 54 ++++++++++++++++++++++++----------------
>  2 files changed, 62 insertions(+), 22 deletions(-)

Nice.

[...]

>  (define (node-load node)
> -  "Return the load on NODE.  Return +ˆ if NODE is misbehaving."
> +  "Return the load on NODE, a normalized value between 0.0 and 1.0.  The value
> +is derived from /proc/loadavg and normalized according to the number of
> +logical cores available, to give a rough estimation of CPU usage.  Return
> +1.0 (fully loaded) if NODE is misbehaving."
>    (let ((line (inferior-eval '(begin
>                                  (use-modules (ice-9 rdelim))
>                                  (call-with-input-file "/proc/loadavg"
>                                    read-string))
> -                             node)))
> -    (if (eof-object? line)
> -        +inf.0 ;MACHINE does not respond, so assume it is infinitely loaded
> +                             node))
> +        (ncores (inferior-eval '(begin
> +                                  (use-modules (ice-9 threads))
> +                                  (current-processor-count))
> +                               node)))
> +    (if (or (eof-object? line) (eof-object? ncores))
> +        1.0    ;MACHINE does not respond, so assume it is fully loaded

Returning 1.0 now is akin to returning + before, meaning that the
machine will never be picked up, is that right?

What if one sets overload-threshold = 1.0, the machine would still be
picked up, no?

> +         (if (and node
> +                  (or (not threshold) (< load threshold))

I think we can assume that THRESHOLD is always a number, including
possible +inf.0.

Thanks,
Ludo.