GNU bug report logs - #67502
[Cuirass] ‘cuirass remote-worker’ gets the CPU count wrong on the OverDrive

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From: Ludovic Courtès <ludovic.courtes <at> inria.fr>
To: 67502 <at> debbugs.gnu.org
Subject: bug#67502: [Cuirass] ‘cuirass remote-worker’ gets the CPU count wrong on the OverDrive
Date: Tue, 28 Nov 2023 10:09:42 +0100

On the OverDrive (AArch64), ‘cuirass remote-worker’ (1.2.0-1.bdc1f9f) says:

  starting 2 workers (parallelism: 1 cores) for server at 10.0.0.1

Instead it should use two cores for each worker:

--8<---------------cut here---------------start------------->8---
ludo <at> dover ~$ guile -c '(use-modules (ice-9 threads)) (pk (current-processor-count))'

;;; (4)
ludo <at> dover ~$ guile -c '(use-modules (ice-9 threads)) (pk (ceiling-quotient (current-processor-count) 2))'

;;; (2)
ludo <at> dover ~$ nproc
4
--8<---------------cut here---------------end--------------->8---

Since ‘current-processor-count’ is implemented indirectly in terms of
‘sched_getaffinity’, this suggests that the process starts with a bogus
affinity mask.  (Time passes…)  That’s indeed the case:

--8<---------------cut here---------------start------------->8---
ludo <at> dover ~$ sudo herd status cuirass-remote-worker
Status of cuirass-remote-worker:
  It is started.
  Running value is 21279.
  It is enabled.
  Provides (cuirass-remote-worker).
  Requires (avahi-daemon guix-daemon networking).
  Will be respawned.
ludo <at> dover ~$ guile -c '(pk (getaffinity 21279))'

;;; (#*1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000)
--8<---------------cut here---------------end--------------->8---

Compare to the affinity mask on x86_64-linux-gnu:

--8<---------------cut here---------------start------------->8---
ludo <at> guix-hpc3 ~$ sudo guile -c '(pk (getaffinity 1817))'

;;; (#*1111111111111111111111111111111100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000)
--8<---------------cut here---------------end--------------->8---

Interesting that the initial affinity mask differs on aarch64-linux-gnu
compared to x86_64-linux-gnu.

Ludo’.

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