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Subject: Re: [PATCH] powerpc: Export PIR data through sysfs
From: Michael Ellerman <michael@ellerman.id.au>
To: Scott Wood <scottwood@freescale.com>
In-Reply-To: <4EB96002.5030605@freescale.com>
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 <4EB96002.5030605@freescale.com>
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Date: Wed, 09 Nov 2011 17:51:24 +1100
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Cc: mahesh@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org,
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On Tue, 2011-11-08 at 10:59 -0600, Scott Wood wrote:
> On 11/08/2011 12:58 AM, Ananth N Mavinakayanahalli wrote:
> > On Mon, Nov 07, 2011 at 11:18:32AM -0600, Scott Wood wrote:
> >> What use does userspace have for this?  If you want to return the
> >> currently executing CPU (which unless you're pinned could change as so=
on
> >> as the value is read...), why not just return smp_processor_id() or
> >> hard_smp_processor_id()?
> >=20
> > Its not just the current cpu. Decoding PIR can tell you the core id,
> > thread id in case of SMT, and this information can be used by userspace
> > apps to set affinities, etc.
>=20
> Wouldn't it make more sense to expose the thread to core mappings in a
> general way, not tied to hardware or what thread we're currently running =
on?

AFAIK that is already available in /sys/devices/system/cpu/cpuX/topology

cheers


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