tree 997946e1157386a0b4b574b5dd37d2f0363b67c7
parent e365aa28d4f30b3d98118ab460c856d3aa72c75e
author Willy Tarreau <w@1wt.eu> 1630141651 +0200
committer Willy Tarreau <w@1wt.eu> 1630142290 +0200
encoding latin1

MINOR: time: add report_idle() to report process-wide idle time

Before threads were introduced in 1.8, idle_pct used to be a global
variable indicating the overall process idle time. Threads made it
thread-local, meaning that its reporting in the stats made little
sense, though this was not easy to spot. In 2.0, the idle_pct variable
moved to the struct thread_info via commit 81036f273 ("MINOR: time:
move the cpu, mono, and idle time to thread_info"). It made it more
obvious that the idle_pct was per thread, and also allowed to more
accurately measure it. But no more effort was made in that direction.

This patch introduces a new report_idle() function that accurately
averages the per-thread idle time over all running threads (i.e. it
should remain valid even if some threads are paused or stopped), and
makes use of it in the stats / "show info" reports.

Sending traffic over only two connections of an 8-thread process
would previously show this erratic CPU usage pattern:

  $ while :; do socat /tmp/sock1 - <<< "show info"|grep ^Idle;sleep 0.1;done
  Idle_pct: 30
  Idle_pct: 35
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 35
  Idle_pct: 33
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100
  Idle_pct: 100

Now it shows this more accurate measurement:

  $ while :; do socat /tmp/sock1 - <<< "show info"|grep ^Idle;sleep 0.1;done
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83
  Idle_pct: 83

This is not technically a bug but this lack of precision definitely affects
some users who rely on the idle_pct measurement. This should at least be
backported to 2.4, and might be to some older releases depending on users
demand.