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offload: Remove the "machine choice" lock. 

This lock was unnecessary and it led to a contention when many 'guix
offload' processes are polling for available machines.

* guix/scripts/offload.scm (machine-choice-lock-file): Remove.
(choose-build-machine): Remove surrounding 'with-file-lock (machine-lock-file)'.
This commit is contained in:
Ludovic Courtès 2018-12-26 17:30:56 +01:00
parent b12f8720f5
commit 7f4d102c2f
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GPG Key ID: 090B11993D9AEBB5
1 changed files with 51 additions and 58 deletions
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guix/scripts/offload.scm
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@ -453,10 +453,6 @@ of free disk space on '~a'~%")
(build-machine-name machine)
"." (symbol->string hint) ".lock"))
(define (machine-choice-lock-file)
"Return the name of the file used as a lock when choosing a build machine."
(string-append %state-directory "/offload/machine-choice.lock"))
(define (random-seed)
(logxor (getpid) (car (gettimeofday))))
@ -479,67 +475,64 @@ of free disk space on '~a'~%")
slot (which must later be released with 'release-build-slot'), or #f and #f."
;; Proceed like this:
;; 1. Acquire the global machine-choice lock.
;; 2. For all MACHINES, attempt to acquire a build slot, and filter out
;; 1. For all MACHINES, attempt to acquire a build slot, and filter out
;; those machines for which we failed.
;; 3. Choose the best machine among those that are left.
;; 4. Release the previously-acquired build slots of the other machines.
;; 5. Release the global machine-choice lock.
;; 2. Choose the best machine among those that are left.
;; 3. Release the previously-acquired build slots of the other machines.
(with-file-lock (machine-choice-lock-file)
(define machines+slots
(filter-map (lambda (machine)
(let ((slot (acquire-build-slot machine)))
(and slot (list machine slot))))
(shuffle machines)))
(define machines+slots
(filter-map (lambda (machine)
(let ((slot (acquire-build-slot machine)))
(and slot (list machine slot))))
(shuffle machines)))
(define (undecorate pred)
(lambda (a b)
(match a
((machine1 slot1)
(match b
((machine2 slot2)
(pred machine1 machine2)))))))
(define (undecorate pred)
(lambda (a b)
(match a
((machine1 slot1)
(match b
((machine2 slot2)
(pred machine1 machine2)))))))
(define (machine-faster? m1 m2)
;; Return #t if M1 is faster than M2.
(> (build-machine-speed m1)
(build-machine-speed m2)))
(define (machine-faster? m1 m2)
;; Return #t if M1 is faster than M2.
(> (build-machine-speed m1)
(build-machine-speed m2)))
(let loop ((machines+slots
(sort machines+slots (undecorate machine-faster?))))
(match machines+slots
(((best slot) others ...)
;; Return the best machine unless it's already overloaded.
;; Note: We call 'node-load' only as a last resort because it is
;; too costly to call it once for every machine.
(let* ((session (false-if-exception (open-ssh-session best)))
(node (and session (remote-inferior session)))
(load (and node (normalized-load best (node-load node))))
(space (and node (node-free-disk-space node))))
(when node (close-inferior node))
(when session (disconnect! session))
(if (and node (< load 2.) (>= space %minimum-disk-space))
(match others
(((machines slots) ...)
;; Release slots from the uninteresting machines.
(for-each release-build-slot slots)
(let loop ((machines+slots
(sort machines+slots (undecorate machine-faster?))))
(match machines+slots
(((best slot) others ...)
;; Return the best machine unless it's already overloaded.
;; Note: We call 'node-load' only as a last resort because it is
;; too costly to call it once for every machine.
(let* ((session (false-if-exception (open-ssh-session best)))
(node (and session (remote-inferior session)))
(load (and node (normalized-load best (node-load node))))
(space (and node (node-free-disk-space node))))
(when node (close-inferior node))
(when session (disconnect! session))
(if (and node (< load 2.) (>= space %minimum-disk-space))
(match others
(((machines slots) ...)
;; Release slots from the uninteresting machines.
(for-each release-build-slot slots)
;; The caller must keep SLOT to protect it from GC and to
;; eventually release it.
(values best slot)))
(begin
;; BEST is unsuitable, so try the next one.
(when (and space (< space %minimum-disk-space))
(format (current-error-port)
"skipping machine '~a' because it is low \
;; The caller must keep SLOT to protect it from GC and to
;; eventually release it.
(values best slot)))
(begin
;; BEST is unsuitable, so try the next one.
(when (and space (< space %minimum-disk-space))
(format (current-error-port)
"skipping machine '~a' because it is low \
on disk space (~,2f MiB free)~%"
(build-machine-name best)
(/ space (expt 2 20) 1.)))
(release-build-slot slot)
(loop others)))))
(()
(values #f #f))))))
(build-machine-name best)
(/ space (expt 2 20) 1.)))
(release-build-slot slot)
(loop others)))))
(()
(values #f #f)))))
(define (call-with-timeout timeout drv thunk)
"Call THUNK and leave after TIMEOUT seconds. If TIMEOUT is #f, simply call