Messages in this thread |  | | | From | Michael Neuling <> | | Subject | Re: [PATCH] sched: Enable arch-specific asym packing option in sched domain | | Date | Sat, 05 May 2012 09:41:40 +1000 |
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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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