Messages in this thread | | | From | Kevin Hilman <> | Subject | Re: [PATCH] nohz1: Documentation | Date | Fri, 22 Mar 2013 11:37:55 -0700 |
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"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes:
> 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 > > ------------------------------------------------------------------------ > > 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).
This is not only the preferred approach, but the *only* approach available on non-x86 systems. Perhaps the others should be marked as x86-only?
Kevin
> 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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