Messages in this thread | | | Date | Thu, 7 Feb 2013 17:25:51 +0100 | Subject | Re: [ANNOUNCE] 3.8-rc6-nohz4 | From | Frederic Weisbecker <> |
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2013/2/7 Ingo Molnar <mingo@kernel.org>: > > * Steven Rostedt <rostedt@goodmis.org> wrote: > >> I'll reply to this as I come up with comments. >> >> First thing is, don't call it NO_HZ_FULL. A better name would >> be NO_HZ_CPU. I would like to reserve NO_HZ_FULL when we >> totally remove jiffies :-) > > I don't think we want yet another config option named in a > weird way. > > What we want instead is to just split NO_HZ up into its > conceptual parts: > > CONFIG_NO_HZ_IDLE
Renaming CONFIG_NO_HZ to CONFIG_NO_HZ_IDLE is something I considered. I was just worried about this option being present in many defconfig. Perhaps we can do that renaming and keep CONFIG_NO_HZ around a little while for backward compatibility (pretty much like what we've done for CONFIG_PERF_COUNTERS -> CONFIG_PERF_EVENTS).
> CONFIG_NO_HZ_USER_SPACE > CONFIG_NO_HZ_KERNEL_SPACE > > Where the current status quo is NO_HZ_IDLE=y, and Frederic is > about to introduce NO_HZ_USER_SPACE=y. When jiffies get removed > we get NO_HZ_KERNEL_SPACE=y.
Note on my tree I stop the tick on both rings. I believe that restarting the tick on kernel entry isn't something we should seriously consider. It would be a costly operation that may make things worse. And in fact there is no big difference. Just kernelspace has more opportunities to be disturbed (RCU IPIs, async timer/work scheduled by the kernel, etc...) and get its tick restarted sometimes.
> > The 'CONFIG_NO_HZ' meta-option, which we should leave for easy > configurability and for compatibility, should get us the > currently recommended default, which for the time being might > be:
Ah looks like you considered the compatibility as well :)
> > CONFIG_NO_HZ_IDLE=y > # CONFIG_NO_HZ_USER_SPACE is disabled > > Btw., you could add CONFIG_NO_HZ_KERNEL_SPACE right away, just > keep it false all the time. That would document our future plans > pretty well. > > Once CONFIG_NO_HZ_USER_SPACE is proven problem-free, we might > default to: > > CONFIG_NO_HZ_IDLE=y > CONFIG_NO_HZ_USER_SPACE=y > > The goal is to have this in the distant future: > > CONFIG_NO_HZ=y > > CONFIG_NO_HZ_IDLE=y > CONFIG_NO_HZ_USER_SPACE=y > CONFIG_NO_HZ_KERNEL_SPACE=y > > And eventually we might even be able to get rid of all the 3 > variants, and only offer full-on/off. > > Agreed?
At least for now we seem to agree on CONFIG_NO_HZ_IDLE and keep CONFIG_NO_HZ for compatibility. Are you ok with that? If so I'll send a patch.
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