Guile's time execution issues

[Aleix Conchillo Flaqué]

Hi,

I was trying to get some guile-json performance times loading large JSON
file. However, I'm getting increasing numbers at each run, so I'm wondering
if I'm doing something wrong. Below you can see how the first run took
19.95s and then running the same command kept increasing.

I'm running Guile 2.2.7 on macOS Catalina 10.15.3.

scheme@(guile-user)> (use-modules (json))
scheme@(guile-user)> ,t (define a (call-with-input-file
"/Users/aleix/Downloads/large-file.json" (lambda (port) (json->scm port))))
;; 19.956429s real time, 87.100982s run time.  75.270202s spent in GC.
;; 26.173179s real time, 143.645265s run time.  131.022631s spent in GC.
;; 28.193926s real time, 154.758375s run time.  141.697236s spent in GC.
;; 29.044218s real time, 160.745984s run time.  147.449073s spent in GC.
;; 30.480873s real time, 170.855527s run time.  157.332793s spent in GC.
;; 30.555700s real time, 172.938278s run time.  159.468737s spent in GC.
;; 32.190478s real time, 172.807551s run time.  158.905645s spent in GC.

The good news is that I have applied a suggestion from Linus Björnstam that
reduces times by half (considering the first run above). The suggestion was
to use string ports instead of string-append. And interestingly this time,
time executions remain around the same value:

scheme@(guile-user)> ,t (define a (call-with-input-file
"/Users/aleix/Downloads/large-file.json" (lambda (port) (json->scm port))))
;; 9.099597s real time, 17.239176s run time.  9.309819s spent in GC.
;; 9.927868s real time, 20.855859s run time.  12.528727s spent in GC.
;; 8.981248s real time, 15.043991s run time.  7.050269s spent in GC.
;; 9.055893s real time, 15.400981s run time.  7.383187s spent in GC.
;; 9.055850s real time, 15.261824s run time.  7.239188s spent in GC.
;; 9.315239s real time, 15.231889s run time.  7.005570s spent in GC.
;; 9.106168s real time, 14.987678s run time.  6.915028s spent in GC.
;; 9.175142s real time, 14.471324s run time.  6.302749s spent in GC.
;; 8.966537s real time, 14.400318s run time.  6.412858s spent in GC.

JSON test data obtained from:

https://github.com/json-iterator/test-data/blob/master/large-file.json

Best,

Aleix