On Thu, Mar 21, 2013 at 10:41:30AM -0700, Arjan van de Ven wrote:
> On 3/21/2013 10:18 AM, Paul E. McKenney wrote:
> > o Use the "idle=poll" boot parameter. However, please note
> > that use of this parameter can cause your CPU to overheat,
> > which may cause thermal throttling to degrade your
> > latencies --and that this degradation can be even worse
> > than that of dyntick-idle.
>
> it also disables (effectively) Turbo Mode on Intel cpus... which can cost you
> a serious percentage of performance
Thank you, added! Please see below for the updated list.
Thanx, Paul
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o Dyntick-idle slows transitions to and from idle slightly.
In practice, this has not been a problem except for the most
aggressive real-time workloads, which have the option of disabling
dyntick-idle mode, an option that most of them take. However,
some workloads will no doubt want to use adaptive ticks to
eliminate scheduling-clock-tick latencies. Here are some
options for these workloads:
a. Use PMQOS from userspace to inform the kernel of your
latency requirements (preferred).
b. Use the "idle=mwait" boot parameter.
c. Use the "intel_idle.max_cstate=" to limit the maximum
depth C-state depth.
d. Use the "idle=poll" boot parameter. However, please note
that use of this parameter can cause your CPU to overheat,
which may cause thermal throttling to degrade your
latencies -- and that this degradation can be even worse
than that of dyntick-idle. Furthermore, this parameter
effectively disables Turbo Mode on Intel CPUs, which
can significantly reduce maximum performance.
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