linux-kernel - Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain

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Message-ID: <20160517111538.GX3193@twins.programming.kicks-ass.net>
Date:	Tue, 17 May 2016 13:15:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Michael Neuling <mikey@...ling.org>,
	Matt Fleming <matt@...eblueprint.co.uk>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, clm@...com, mgalbraith@...e.de,
	tglx@...utronix.de, fweisbec@...il.com, anton@...ba.org,
	oliver <oohall@...il.com>,
	"Shreyas B. Prabhu" <shreyas@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with
 sched_domain_shared

On Tue, May 17, 2016 at 04:22:04PM +0530, Srikar Dronamraju wrote:
> > 
> > Maybe even something like so; which would make Power <= 6 use the
> > default topology and result in a shared LLC between the on package cores
> > etc..
> > 
> > Power7 is then special for not having a shared L3 but having the
> > asymmetric SMT thing and Power8 again gains the shared L3 while
> > retaining the asymmetric SMT stuff.
> 
> 
> Asymmetric SMT is only for Power 7. Its not enabled for Power 8.
> On Power8, if there are only 2 active threads assume thread 0 and thread
> 4 running in smt 8 mode, it would internally run as if running in smt 2
> mode without any scheduler tweaks. (This is unlike power 7).

Ah, good to know. In that case, you can use the generic topology for
everything except power7. IOW, just make that existing
set_sched_topology() call depend on CPU_FTRS_POWER7 or so (if that is
the correct magic incantation).