Don't let perftune.py print false alarm error message when we calculate
a compute CPU set for tuning modes.
This may happen when we calculate a CPU set for non-MQ tuning modes on
small systems on which these modes are forbidden because they would
result in a zero CPU set, e.g. sq_split on a system with a single
physical core.
We are going to utilize a newly introduced --get-cpu-mask-quiet execution
mode introduced to the seastar/script/perftune.py by the
"perftune.py: introduce --get-cpu-mask-quiet" series which would return
a zero CPU set if that's what it turns out to be instead of exiting with
an error what --get-cpu-mask would do in such a case.
The rest of scylla_util.py logic is going to handle a zero CPU set
returned by get_mode_cpuset() correctly.
Fixes#4211Fixes#4443
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Message-Id: <20190731212901.9510-1-vladz@scylladb.com>
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