From: Diwakar Tundlam <dtundlam@nvidia.com>
To: "'Michael Neuling'" <mikey@neuling.org>
CC: "'Peter Zijlstra'" <a.p.zijlstra@chello.nl>,
        "'Ingo Molnar'" <mingo@kernel.org>,
        "'Andrew Morton'" <akpm@linux-foundation.org>,
        "'Christoph Lameter'" <cl@gentwo.org>,
        "'Stephen Rothwell'" <sfr@canb.auug.org.au>,
        "'Benjamin Herrenschmidt'" <benh@kernel.crashing.org>,
        "'David Rientjes'" <rientjes@google.com>,
        "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
        Peter De Schrijver <pdeschrijver@nvidia.com>
Date: Fri, 4 May 2012 16:25:16 -0700
Subject: RE: [PATCH] sched: Enable arch-specific asym packing option in
 sched domain
Thread-Topic: [PATCH] sched: Enable arch-specific asym packing option in
 sched domain
Thread-Index: Ac0qTIR81dajrD3zSfyfaTGtipVnygAACJrQ
Message-ID: <1DD7BFEDD3147247B1355BEFEFE46652379C3DF104@HQMAIL04.nvidia.com>
References: <1DD7BFEDD3147247B1355BEFEFE46652379C3DF0FF@HQMAIL04.nvidia.com>
 <1DD7BFEDD3147247B1355BEFEFE46652379C3DF101@HQMAIL04.nvidia.com>
 <1336169422.16236.1.camel@twins>
 <1DD7BFEDD3147247B1355BEFEFE46652379C3DF102@HQMAIL04.nvidia.com>
 <1336170586.16236.11.camel@twins>
 <1DD7BFEDD3147247B1355BEFEFE46652379C3DF103@HQMAIL04.nvidia.com>
 <19500.1336173634@neuling.org>
In-Reply-To: <19500.1336173634@neuling.org>
Accept-Language: en-US
Content-Language: en-US
acceptlanguage: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3430
Lines: 81

>> 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.

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?
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/