I'm running a large server with 192 cores. Consequently, /var/log/messages gets cluttered with messages of started and finished tasks.

Is there a setting somewhere which would use a different file for this output, or suppress it altogether?

I'm running a large server with 192 cores. Consequently, /var/log/messages gets cluttered with messages of started and finished tasks.

Is there a setting somewhere which would use a different file for this output, or suppress it altogether?

What logging facility does that server use? If it is rsyslog (most likely), as root create /etc/rsyskog.d/boinc.frule as follows:

if ($programname == 'boinc') \
then {
-/var/log/boinc-client.log
stop
}

If you wish to suppress boinc logging (not really recommended, unless you are certain you will never have a problem), then simply omit the filename:

if ($programname == 'boinc') \
then {
stop
}

In either instance, it will be necessary to reload the rsyslog service: systemctl reload rsyslog.service