Messages in this thread | | | Date | Thu, 21 Mar 2013 11:02:18 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] nohz1: Documentation |
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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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