linux-kernel - Re: [patch v2 21/30] x86/cpu/topology: Use topology bitmaps for sizing

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Date: Sun, 28 Jan 2024 12:01:14 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: "Zhang, Rui" <rui.zhang@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Raj, Ashok" <ashok.raj@...el.com>,
	"mhklinux@...look.com" <mhklinux@...look.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"ray.huang@....com" <ray.huang@....com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>,
	"andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
	"Sivanich, Dimitri" <dimitri.sivanich@....com>,
	"Tang, Feng" <feng.tang@...el.com>,
	"kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
	"Mehta, Sohil" <sohil.mehta@...el.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"kprateek.nayak@....com" <kprateek.nayak@....com>,
	"jgross@...e.com" <jgross@...e.com>,
	"andy@...radead.org" <andy@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [patch v2 21/30] x86/cpu/topology: Use topology bitmaps for
 sizing

On Fri, Jan 26, 2024 at 09:22:47PM +0100, Thomas Gleixner wrote:
> On Fri, Jan 26 2024 at 07:07, Zhang, Rui wrote:
> >> >  
> >> > +       cnta = domain_weight(TOPO_PKG_DOMAIN);
> >> > +       cntb = domain_weight(TOPO_DIE_DOMAIN);
> >> > +       __max_logical_packages = cnta;
> >> > +       __max_dies_per_package = 1U << (get_count_order(cntb) - >
> >> > get_count_order(cnta));
> >> > +
> >> > +       pr_info("Max. logical packages: %3u\n", cnta);
> >> > +       pr_info("Max. logical dies:     %3u\n", cntb);
> >> > +       pr_info("Max. dies per package: %3u\n", >
> >> > __max_dies_per_package);
> >> > +
> >> > +       cnta = domain_weight(TOPO_CORE_DOMAIN);
> >> > +       cntb = domain_weight(TOPO_SMT_DOMAIN);
> >> > +       smp_num_siblings = 1U << (get_count_order(cntb) - >
> >> > get_count_order(cnta));
> >> > +       pr_info("Max. threads per core: %3u\n", smp_num_siblings);
> >> > +
> >
> > I missed this but Ashok catches it.
> >
> > Say, on my Adlerlake platform, which has 4 Pcores with HT + 8 Ecores,
> > cnta is 12, cntb is 16, and smp_num_siblings is set to 1 erroneously.
> >
> > I think we should use
> > 	smp_num_siblings = DIV_ROUND_UP(cntb, cnta);
> > here.
> 
> Indeed. That's more than obvious.
> 
> > Or even check each core to get the maximum value (in case there are
> > more than 2 siblings in a core some day).
> 
> We want to get rid of HT not make it worse.

Hear, hear!!!  ;-)

							Thanx, Paul