linux-kernel - Re: [PATCH v2 6/6 RFT] sched/fair: change sched asym checking condition

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Date: Thu, 1 Feb 2024 08:33:30 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: kuiliang Shi <seakeel@...il.com>, alexs@...nel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/6 RFT] sched/fair: change sched asym checking
 condition

On Thu, Feb 01, 2024 at 08:49:05PM +0530, Shrikanth Hegde wrote:
> 
> 
> On 2/1/24 5:10 PM, kuiliang Shi wrote:
> > 
> > 
> > On 2/1/24 9:10 AM, Ricardo Neri wrote:
> >> On Tue, Jan 30, 2024 at 09:17:08PM +0800, alexs@...nel.org wrote:
> >>> From: Alex Shi <alexs@...nel.org>
> >>>
> >>> Asym only used on SMT sd, or core sd with ITMT and core idled.
> >>> !sched_smt_active isn't necessary.
> >>
> >> sched_smt_active() is implemented as a static key. Thus, if SMT is not
> >> enabled, we can quickly return without having to check the rest of the
> >> conditions, as we should.
> > 
> > Hi Ricardo,
> > 
> > Thanks a lot for comments! I will drop this patch in this series.
> > 
> > But forgive my stupidity, asym feature is possible when SMT enabled instead of SMT disable. Why no SMT is a condition for asm feature? For this asym feature, I only see the SMT and MC domain use this, correct me if I'm wrong. 
> > 
> 
> on power7 ASYM_PACKING is used to pack at SMT level. 

Indeed, this is why the function returns true if it the sched domain has
the SD_SHARE_CPUCAPACITY flag.

When SMT is disabled there is no point in doing any check because we will
always want to use asym_packing.

> 
> On x86, ITMT topology uses ASYM_PACKING to do load balancing instead of using different cpu capacities.

You can look at x86_cluster_flags() and x86_die_flags().

> 
> Its possible to have it in PKG(earlier referred as DIE) as well. 
> In powerpc recently we did that for shared processor LPAR's. So asym feature is in PKG as well. 
> 
> >>
> >>>