linux-kernel - Re: [ANNOUNCE] 3.9-rc1-nohz1

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Date:	Sat, 9 Mar 2013 09:26:50 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Kevin Hilman <khilman@...aro.org>,
	Mats Liljegren <mats.liljegren@...a.com>
Subject: Re: [ANNOUNCE] 3.9-rc1-nohz1


* Frederic Weisbecker <fweisbec@...il.com> 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://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.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?

Thanks,

	Ingo
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