Messages in this thread | | | Date | Tue, 05 Jun 2012 23:35:35 +0800 | From | Jiang Liu <> | Subject | Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi |
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Hi Thomas, It's a great idea to use state machine to implement cpu online/offline. Actually we are trying to split the cpu online/offline flow into several stages so we could do error recover easily when hot-plugging physical processors. Thanks! Gerry
On 06/05/2012 04:11 AM, Thomas Gleixner wrote: > On Mon, 4 Jun 2012, Fenghua Yu wrote: > >> From: Fenghua Yu <fenghua.yu@intel.com> >> >> Since offline CPU is in wmait or hlt if mwait feature is not available, it can >> be waken up by writing to monitored memory range or via nmi. >> >> Compared to current INIT, INIT, STARTUP wake up sequence, waking up offline CPU >> is faster via wmait or nmi. This is especially useful when offline CPU for >> power saving and shorter waking up time is desired. On one tested desktop >> machine, waking up time via mwait or nmi is reduced to 23% of waking up time >> via INIT. Waking up time is measured from the beginning of store_online() to >> the beginning of cpu_idle() after the CPU is waken up. >> >> Waking up offline CPU via mwait or nmi is also useful to support BSP offline/ >> online because offline BSP can not be waken up by the INIT's sequence. The BSP >> offline/online patchset will be sent out seperately. > > I understand what you are trying to do, though I completely disagree > with the solution. > > The main problem of the current hotplug code is that it is an all or > nothing approach. You have to tear down the whole thing completely > instead of just taking it out of the usable set of cpus. > > I'm working on a proper state machine driven online/offline sequence, > where you can put the cpu into an intermediate state which avoids > bringing it down completely. This is enough to get the full > powersaving benefits w/o having to go through all the synchronization > states of a full online/offline. That will shorten the onlining time > of an previously offlined cpu to almost nothing. > > I really want to avoid adding more bandaids to the hotplug code before > we have sorted out the existing horror. > > Thanks, > > tglx > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.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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