We set the scheduler wakeup granularity to 500usec, because that is the
difference in runtime we want to see from a waking task before it
preempts the running task (which will usually be Scylla). Scheduling
other processes less often is usually good for Scylla, but in this case,
one of the "other processes" is also a Scylla thread, the one we have
been using for marking ticks after we have abandoned signals.
However, there is an artifact from the Linux scheduler that causes those
preemption to be missed if the wakeup granularity is exactly twice as
small as the sched_latency. Our sched_latency is set to 1ms, which
represents the maximum time period in which we will run all runnable
tasks.
We want to keep the sched_latency at 1ms, so we will reduce the wakeup
granularity so to something slightly lower than 500usec, to make sure
that such artifact won't affect the scheduler calculations. 499.99usec
will do - according to my tests, but we will reduce it to a round
number.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <20170427135039.8350-1-glauber@scylladb.com>
On NUMA hardware, autonuma may reduce performance by
unmapping memory.
Since we do manual NUMA placement, autonuma will not
help anything.
We ought to disable it by setting the kernel.numa_balancing
sysctl to 0.
Fixes: #1120
Signed-of-by: Benoît Canet <benoit@scylladb.com>
Message-Id: <1466006345-9972-1-git-send-email-benoit@scylladb.com>
Scylla-jmx and collectd can preempt scylla and induce long latencies. Tune
the scheduler to provide lower latencies.
Since when the support processes are not running we normally do not context
switch (one thread per core, remember?), there should be no effect on
throughput.
The tunings are provided in a separate package, which can be uninstalled
if the server is shared with other applications which are negatively
affected by the tuning.
Fixes#1218.
Message-Id: <1464529625-12825-1-git-send-email-avi@scylladb.com>
