On Thu, 2013-02-07 at 12:10 +0100, Ingo Molnar wrote: > * Steven Rostedt <rost...@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 > 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.
Saying NO_HZ_USER_SPACE is a bit of a misnomer. As we don't just stop the tick for user space, but it may remained stopped when entering the kernel. The rule is that when there's just a single task on a CPU, the tick can stop (no scheduling work needed). But if the task triggers something that may require a tick (like printk) then the tick will start again. But just going into the kernel does not designate a tick restart. Maybe a better name would be NO_HZ_SINGLE_TASK ? > > 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: > > 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. Maybe the removal of jiffies would be NO_HZ_COMPLETE? -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
