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Date: Mon, 16 Nov 2015 16:00:31 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Jacob Pan <jacob.jun.pan@...ux.intel.com> Cc: Arjan van de Ven <arjan@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, John Stultz <john.stultz@...aro.org>, LKML <linux-kernel@...r.kernel.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Len Brown <len.brown@...el.com>, Rafael Wysocki <rafael.j.wysocki@...el.com>, Eduardo Valentin <edubezval@...il.com>, Paul Turner <pjt@...gle.com>, Josh Triplett <josh@...htriplett.org> Subject: Re: [PATCH 2/4] timer: relax tick stop in idle entry On Mon, Nov 16, 2015 at 03:40:46PM -0800, Jacob Pan wrote: > On Mon, 16 Nov 2015 15:32:38 -0800 > Arjan van de Ven <arjan@...ux.intel.com> wrote: > > > On 11/16/2015 3:28 PM, Paul E. McKenney wrote: > > > > > Is this mostly an special-purpose embedded thing, or do you expect > > > distros to be enabling this? If the former, I suggest > > > , but if distros are doing this for > > > general-purpose workloads, I instead suggest CONFIG_RCU_FAST_NO_HZ. > > > > thermal overload happens a lot on small devices, but sadly also in > > big datacenters where it is not uncommon to underprovision cooling > > capacity by a bit (it's one of those "99% of the time you only need > > THIS much, the 1% you need 30% more" and that more is expensive or > > even impractical) Then CONFIG_RCU_FAST_NO_HZ it is. > CONFIG_RCU_FAST_NO_HZ is more inline with idle injection in that both > are targeted energy efficiency. > Checking ubuntu and fedora, seems both have CONFIG_RCU_NOCB_CPU_ALL=y. Ah, that is right -- they both do CONFIG_NO_HZ_FULL=y, which does imply CONFIG_RCU_NOCB_CPU_ALL=y. But SUSE does not, last I knew. But it should be easy to set up Kconfig for this. Make your new Kconfig option select CONFIG_RCU_FAST_NO_HZ unless CONFIG_RCU_NOCB_CPU_ALL is already set. Alternatively, CONFIG_RCU_FAST_NO_HZ could be set up something like the following: depends on (NO_HZ_COMMON && SMP && RCU_EXPERT) || CONFIG_THERM_THROT default CONFIG_THERM_THROT But the "select RCU_FAST_NO_HZ if !RCU_NOCB_CPU_ALL" is probably cleaner. Anyway, again, the details can be settled later. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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