Usage of filter breaks "on_interval" for chisels

[scrwr]

Once you add a filter, chisels "on_interval" is triggered with weird timings.

The following minimal chisel shows the effect.

description = "Test chisel with interval"
short_description = "Test chisel"
category = "misc"

args = {}

function on_capture_start()
	chisel.set_interval_ns(500000000)
	return true
end

function on_interval(ts_s, ts_ns, delta)
  print("delta:" .. delta)
  return true
end

Called without filter:

# sudo sysdig -c intervaltest
delta:0
delta:510949747
delta:483104217
delta:500873072
delta:500560051

Called with filter:

# sudo sysdig -c intervaltest "proc.name=systemd"
delta:0
delta:486482802
delta:-2541701
delta:2541701
delta:501229162
delta:508373385
delta:-12144248
delta:12144248
delta:488501703
delta:500266345
delta:-912296
delta:912296

sysdig --version

sysdig version 0.26.4

uname -a

Linux hostname 5.3.0-40-generic #32-Ubuntu SMP Fri Jan 31 20:24:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

[github-actions[bot]]

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[scrwr]

Checked recently, the issue is still existing.