Re: [ANNOUNCE] 3.9-rc1-nohz1

From: Ingo Molnar
Date: Sat Mar 09 2013 - 03:27:17 EST

* Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:

> Hi,
> Several fixes there. And this version should have much lesser spurious warnings.
> Your testing and reviews is very appreciated.
> The 5 first patches of the series are pending on a pull request for -tip (3.10
> material).
> I'm now considering how I should upstream the rest of the series. All the pieces
> that got merged until now were sort of easy because the various chunks were pretty
> self contained and independant (full dynticks cputime accounting, printk, RCU user
> mode, dynticks API generalization, etc...).
> Now what remains in this series is hard to cut into individual parts. Everything
> depends on defining an interface with kernel parameter to partition the full
> dynticks CPUs set.
> I think we really need to start using a branch in -tip and move incrementally from
> there with the following steps:
> 1) Set the kernel parameters and config option
> 2) Handle timers wakeup, timekeeping, posix cpu timers, perf, sched etc...
> on top of kernel parameter based CPU partition
> 3) Once we know _everything_ is handled, bring the final dynticks infrastructure
> 4) Upstream
> This will make everything much easier for everyone: easier piecewise reviews and
> easier for other people to contribute.
> Because you don't want me to spam you with ~40 commits for 2 more years, right?
> Thanks.
> This version can be found at:
> git://
> 3.9-rc1-nohz1
> ---
> Changes since 3.8-rc6-nohz4:
> * Rebase against 3.9-rc1
> * Fixed a few races with exception and preemption handling [1-3/29]
> * Dropped commit "sched: Remove broken check for skip clock update"
> that was buggy (thanks Steve for pointing that)
> * Ignore noisy stale rq clock detection on boot and other situations
> with rq->skip_clock_update [27/29]
> * Dropped commit "sched: Update clock of nohz busiest rq before balancing"
> that became useless (thanks Li Zhong)
> * Don't issue a self IPI on timer enqueue if the CPU didn't stop its
> tick [9/29]
> * Rename a bit the Kconfig menu after discussion with Borislav [6/29]
> * Handle broken full_nohz mask in kernel parameters (thanks Borislav) [6/29]
> ---
> TODO list hasn't changed much:
> - Posix CPU timers
> - Perf events
> - sched_class::task_tick()
> - various other scheduler details
> - ...

We could certainly start tip:sched/dynticks (or tip:timers/dynticks) to accelerate
the upstream merging of it. Nobody expressed deep concerns with the approach, so
what is left is some more hard work.

Two quick requests:

- Mind adding a Documentation/... file with a high level description,
rough design, open problems, etc.?

- Please outline how the current TODO entries affect upstream
mergability. Does it reduce the 'full'-ness of this dynticks mode?
Outright buggy behavior? Other trade-offs?


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