Hi Jan-Henrik:
Thank you for the response. That explains the temporary CPU spike.
Following is the rule where the exec action runs 'foo' which does nothing:
check program syslog-check with path "/sbin/service rsyslog status"
if status = 0 then
exec "/mnt/scripts/foo up"
if status != 0 then
exec "/mnt/scripts/foo down"
There are 20 of those 'check programs' that run 'foo' with a different
path every 30 seconds.
Is there anything that can be tuned to alleviate the "temporary" CPU
spike under this scenario?
Thanks,
Bill
On 03/17/2016 03:59 PM, Jan-Henrik Haukeland wrote:
> A standard exec action is performed with spawn() which you can investigate
> here,
> https://bitbucket.org/tildeslash/monit/src/80ce931b4f4e4dc0324d0bd290cd7fc50c741c87/src/spawn.c?at=master&fileviewer=file-view-default
>
> This is basically a standard fork->exec (with a twist) which you can also see
> in posix_spawn etc. Three things to note, 1) a fork->exec is “expensive” in
> computing terms, but this is also what your OS or shell does when it starts a
> new program. I.e. it is a standard operation. 2) Seeing a CPU spike at
> program startup, especially when done 20 times in a short timeframe is to be
> expected. If the CPU usage goes back to normal fairly quick it is nothing to
> worry about. 3) In Monit, “if X then exec ..” is meant to be used in out of
> bounds situations and if you have 20 execs you should probably tune ‘X’
> above.
>
> Ps. "check program”, start and restart executes in a slightly different way
>
>
>> On 17 Mar 2016, at 22:58, Bill Durant <[email protected]> wrote:
>>
>> Hello:
>>
>> How does Monit perform the exec action internally?
>>
>> I am finding that running too many "exec" actions during a polling
>> interval causes a high system CPU usage spike.
>>
>> I am able to duplicate the CPU spike by having Monit run 20 exec actions
>> at every 30 second polling interval even it runs a program that does
>> nothing such as the following:
>>
>> $ cat foo.c
>> main(){}
>>
>> $ cc -c foo foo.c
>>
>> So when Monit runs "foo" 20 times via the exec action, at every polling
>> interval, the system CPU usage jumps to 90%+.
>>
>> And staggering the exec's with a 'run every N cycles' or 'run every cron
>> xxx' appears to not guarantee that the number of exec's run on every
>> polling cycle will be minimized.
>>
>> Is the exec action heavy weight by design?
>>
>> Thanks,
>>
>> Bill
>>
>>
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