Messages in this thread | | | Date | Wed, 29 May 2013 23:29:09 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC PATCH v3 0/5] powerpc: Support context tracking for Power pSeries |
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On Mon, May 13, 2013 at 04:03:13PM +0800, Li Zhong wrote: > On Mon, 2013-05-13 at 15:51 +1000, Benjamin Herrenschmidt wrote: > > On Mon, 2013-05-13 at 13:21 +0800, Li Zhong wrote: > > > These patches try to support context tracking for Power arch, beginning with > > > 64-bit pSeries. The codes are ported from that of the x86_64, and in each > > > patch, I listed the corresponding patch for x86. > > > > So that's yet another pile of bloat on all syscall entry/exit and > > exception entry/exit. What is it used for ? (I haven't followed on > > x86_64 side). > > To my understanding, it is used to enable RCU user extended quiescent > state, so RCU on that cpu doesn't need scheduler ticks. And together > with some other code(already in 3.10), we are able to remove the ticks > in some cases (e.g. only 1 task running on the cpu, with some other > limitations). > > Maybe Paul, or Frederic could give some better descriptions.
That's pretty much it. It helps RCU and cputime accounting infrastructure to know when we enter/exit userspace. This way we can:
* Consider the CPU as idle from an RCU point of view when we run in userspace, so RCU won't need the tick to stay alive.
* Account cputime (utime/stime/...) without using the tick. Ok powerpc already has CONFIG_VIRT_CPU_ACCOUNTING_NATIVE but making it working with full dynticks would require some tweaks.
All in one this is to support full dynticks.
Thanks.
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