linux-kernel - Re: [RFC GIT PULL] nohz: Basic cputime accounting for adaptive tickless

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Date:	Fri, 15 Jun 2012 14:13:25 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Kevin Hilman <khilman@...com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"Luck,Tony" <tony.luck@...el.com>
Subject: Re: [RFC GIT PULL] nohz: Basic cputime accounting for adaptive
 tickless


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Thu, Jun 14, 2012 at 04:36:33PM +0200, Ingo Molnar wrote:
> > 
> > * Frederic Weisbecker <fweisbec@...il.com> wrote:
> > 
> > > > > > > > I'll try something with that.
> > > > > > > 
> > > > > > > Maybe sanitize all the variants under a single set of 
> > > > > > > wrappers/callbacks?
> > > > > > 
> > > > > > Yes, please!
> > > > > 
> > > > > Sure, I'm working in it.
> > > >  
> > > > Please keep me in the loop, I want to avoid that things 
> > > > break on s390. Thanks.
> > > 
> > > Well, I realize I can't consolidate much between ia64, s390 
> > > and ppc because they all handle virtual cpu time accounting 
> > > very differently. I'm also not what the virtual timer is for.
> > 
> > As a first step I'd suggest to create a superset of all existing 
> > and relied-upon wrappers/callbacks, into a single obvious 
> > sched_*() or time_*() namespace, without breaking functionality.
> 
> But the API is already well defined. The arch just need to 
> implement account_system_vtime() and account_process_tick() 
> and record the time on the kernel boundaries. This is pretty 
> well contained in ppc entry.S where it is implemented through 
> ACCOUNT_CPU_USER_ENTRY/EXIT macros (although I see the time 
> accounted on syscall boundaries but not in exceptions), it's 
> more complicated in ia64 as the virt accounting is spread here 
> and there in entry.S and it's always on in s390.
> 
> May be we could standardize a bit the way we save and account 
> the time. This require some non-trivial asm surgery on archs I 
> don't know much about though.

Yeah, account_*() is a fine API too - as long as it's a 
unification of all time accounting functionality.

Thanks,

	Ingo
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