linux-kernel - Re: [RFC][PATCH v5 01/14] sched: add a new arch_sd_local_flags for sched

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Message-ID: <20131106140807.GM10651@twins.programming.kicks-ass.net>
Date:	Wed, 6 Nov 2013 15:08:07 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"cmetcalf@...era.com" <cmetcalf@...era.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	Alex Shi <alex.shi@...el.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <len.brown@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Lukasz Majewski <l.majewski@...sung.com>,
	james.hogan@...tec.com, heiko.carstens@...ibm.com
Subject: Re: [RFC][PATCH v5 01/14] sched: add a new arch_sd_local_flags for
 sched_domain init

On Wed, Nov 06, 2013 at 02:53:44PM +0100, Martin Schwidefsky wrote:
> On Tue, 5 Nov 2013 23:27:52 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Nov 05, 2013 at 03:57:23PM +0100, Vincent Guittot wrote:
> > > Your proposal looks fine for me. It's clearly better to move in one
> > > place the configuration of sched_domain fields. Have you already got
> > > an idea about how to let architecture override the topology?
> > 
> > Maybe something like the below -- completely untested (my s390 compiler
> > is on a machine that's currently powered off).
> 
> In principle I do not see a reason why this should not work, but there
> are a few more things to take care of. E.g. struct sd_data is defined
> in kernel/sched/core.c, cpu_cpu_mask as well. These need to be moved
> to a header where arch/s390/kernel/smp.c can pick it up.
> 
> I do have the feeling that the sched_domain_topology should be left
> where they are, or do we really want to expose more of the scheduler
> internals?

Ah, its a trade off; in that previous patch I removed the entire
sched_domain initializers the archs used to 'have' to fill out. That
exposed far too much behavioural stuff the archs really shouldn't
bother with.

In return we now provide a (hopefully) simpler interface that allows
archs to communicate their topology to the scheduler -- without getting
mixed up in the behavioural aspects (too much).

Maybe s390 wasn't the best example to pick, as the book domain really
isn't that exciting. Arguably I should have taken Power7+ and the
ASYM_PACKING SMT thing.


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