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SubjectRe: [PATCH] sched: Enable arch-specific asym packing option in sched domain
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Diwakar Tundlam <dtundlam@nvidia.com> wrote:

> >> Arrh, so it's not a performance issue but power savings.. that would this asymmetric packing a lot more appropriate to use.
>
> Yes, it is for power saving..
>
> Could you suggest a way t use this flag without affecting Power7, then?
> I was thinking to define a different weak arch_sd_package_asym_packing() in SD_CPU_INIT.
> And the flag is set only for arch/arm/mach-tegra/tegra3.

That would work but Peter knows much better than me.

Mikey

>
> Thanks,
> --Diwakar.
>
> -----Original Message-----
> From: Michael Neuling [mailto:mikey@neuling.org]
> Sent: Friday, May 04, 2012 4:21 PM
> To: Diwakar Tundlam
> Cc: 'Peter Zijlstra'; 'Ingo Molnar'; 'Andrew Morton'; 'Christoph Lameter'; 'Stephen Rothwell'; 'Benjamin Herrenschmidt'; 'David Rientjes'; 'linux-kernel@vger.kernel.org'; Peter De Schrijver
> Subject: Re: [PATCH] sched: Enable arch-specific asym packing option in sched domain
>
> > Thanks for clarifying the Power7. I see the point - package vs cpu's within a package.
> >
> > Yes, this is for Nvidia's ARM Quad-core Tegra CPU. It is a single
> > package, organized flatly. To save power, we want cores to be loaded
> > up in order from cpu0, 1, etc. The ASYM_PACKING flag seems to do
> > exactly what we need if set in the domain flag.
>
> Arrh, so it's not a performance issue but power savings.. that would this asymmetric packing a lot more appropriate to use.
>
> Mikey
>
> >
> > Thanks,
> > --Diwakar.
> >
> > -----Original Message-----
> > From: Peter Zijlstra [mailto:a.p.zijlstra@chello.nl]
> > Sent: Friday, May 04, 2012 3:30 PM
> > To: Diwakar Tundlam
> > Cc: 'Ingo Molnar'; 'Andrew Morton'; 'Christoph Lameter'; 'Michael
> > Neuling'; 'Stephen Rothwell'; 'Benjamin Herrenschmidt'; 'David
> > Rientjes'; 'linux-kernel@vger.kernel.org'; Peter De Schrijver
> > Subject: RE: [PATCH] sched: Enable arch-specific asym packing option
> > in sched domain
> >
> > On Fri, 2012-05-04 at 15:18 -0700, Diwakar Tundlam wrote:
> > >
> > > arch_sd_sibling_asym_packing() is already present under ifdef CONFIG_SMT.
> > > I didn't touch that. I only added it to SD_CPU_INIT for all cpu's.
> > > I assumed Power7 shouldn't use SD_CPU_INIT.
> >
> > All archs use SD_CPU_INIT, its the default topology level for a package/socket. So now you've made Power7 prefer lower numbered sockets over higher numbered sockets.. not fatal, but not really nice either.
> >
> > [ power7 is the only one that implements arch_sd_sibling_asym_packing
> > ]
> >
> > > Maybe I should define a separate weak symbol, say arch_sd_bias_to_lower_num_cpu()?
> > > Then Power7 can define arch_sd_sibling_asym_packing() to be '1' and
> > > it will not break all-cpu init.
> >
> > A slightly saner name would be:
> >
> > arch_sd_package_asym_packing()
> >
> > FWIW, I suspect you're wanting to use this for some ARM chip (nvidia
> > doesn't do much else -- aside from this graphics stuff) so that if
> > there's hardly anything it runs on cpu0. Now, last time I checked,
> > these ARM things had only 1 package, so I still don't see the point
> > :-)
> >
> > I suspect you want to modify SD_MC_INIT() with something like:
> >
> > arch_sd_mc_asym_packing()
> >
> > Or is this the big-little thing and you're representing them as separate packages?
> >
> > See how a little extra information avoids me having to endlessly second guess wtf you're actually wanting to do?
> >
>


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