linux-kernel - Re: [PATCH v3 1/2] x86/smpboot: Decrapify build_sched

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <197be36341f.121c2d667978523.290703926590546064@linux.beauty>
Date: Mon, 30 Jun 2025 08:21:52 +0800
From: Li Chen <me@...ux.beauty>
To: "Peter Zijlstra" <peterz@...radead.org>
Cc: "Thomas Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...hat.com>,
	"Borislav Petkov" <bp@...en8.de>,
	"Dave Hansen" <dave.hansen@...ux.intel.com>, "x86" <x86@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	"K Prateek Nayak" <kprateek.nayak@....com>,
	"Sohil Mehta" <sohil.mehta@...el.com>,
	"Brian Gerst" <brgerst@...il.com>,
	"Patryk Wlazlyn" <patryk.wlazlyn@...ux.intel.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Li Chen" <chenl311@...natelecom.cn>
Subject: Re: [PATCH v3 1/2] x86/smpboot: Decrapify build_sched_topology()

Hi Peter,


 ---- On Wed, 25 Jun 2025 16:28:19 +0800  Peter Zijlstra <peterz@...radead.org> wrote --- 
 > On Wed, Jun 25, 2025 at 11:45:49AM +0800, Li Chen wrote:
 > > From: Thomas Gleixner <tglx@...utronix.de>
 > > 
 > > The #ifdeffery and the initializers in build_sched_topology() are just
 > > disgusting. The SCHED_SMT #ifdef is also pointless because SCHED_SMT is
 > > unconditionally enabled when SMP is enabled.
 > 
 > On x86, but not across all archs. Yes this is x86 code, but how is one
 > supposed to keep all that nonsense straight in their head ;-)
 > 
 > > Statically initialize the domain levels in the topology array and let
 > > build_sched_topology() invalidate the package domain level when NUMA in
 > > package is available.
 > > 
 > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
 > > ---
 > >  arch/x86/kernel/smpboot.c | 45 +++++++++++++++------------------------
 > >  1 file changed, 17 insertions(+), 28 deletions(-)
 > > 
 > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
 > > index fc78c2325fd29..7d202f9785362 100644
 > > --- a/arch/x86/kernel/smpboot.c
 > > +++ b/arch/x86/kernel/smpboot.c
 > > @@ -478,43 +478,32 @@ static int x86_cluster_flags(void)
 > >   */
 > >  static bool x86_has_numa_in_package;
 > >  
 > > -static struct sched_domain_topology_level x86_topology[6];
 > > +#define DOMAIN(maskfn, flagsfn, dname) { .mask = maskfn, .sd_flags = flagsfn, .name = #dname }
 > >  
 > > -static void __init build_sched_topology(void)
 > > -{
 > > -    int i = 0;
 > > -
 > > -#ifdef CONFIG_SCHED_SMT
 > > -    x86_topology[i++] = (struct sched_domain_topology_level){
 > > -        cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT)
 > > -    };
 > > -#endif
 > > +static struct sched_domain_topology_level x86_topology[] = {
 > > +    DOMAIN(cpu_smt_mask, cpu_smt_flags, SMT),
 > >  #ifdef CONFIG_SCHED_CLUSTER
 > > -    x86_topology[i++] = (struct sched_domain_topology_level){
 > > -        cpu_clustergroup_mask, x86_cluster_flags, SD_INIT_NAME(CLS)
 > > -    };
 > > +    DOMAIN(cpu_clustergroup_mask, x86_cluster_flags, CLS),
 > >  #endif
 > >  #ifdef CONFIG_SCHED_MC
 > > -    x86_topology[i++] = (struct sched_domain_topology_level){
 > > -        cpu_coregroup_mask, x86_core_flags, SD_INIT_NAME(MC)
 > > -    };
 > > +    DOMAIN(cpu_coregroup_mask, x86_core_flags, MC),
 > >  #endif
 > > -    /*
 > > -     * When there is NUMA topology inside the package skip the PKG domain
 > > -     * since the NUMA domains will auto-magically create the right spanning
 > > -     * domains based on the SLIT.
 > > -     */
 > > -    if (!x86_has_numa_in_package) {
 > > -        x86_topology[i++] = (struct sched_domain_topology_level){
 > > -            cpu_cpu_mask, x86_sched_itmt_flags, SD_INIT_NAME(PKG)
 > > -        };
 > > -    }
 > > +    DOMAIN(cpu_cpu_mask, x86_sched_itmt_flags, PKG),
 > > +    { NULL },
 > > +};
 > >  
 > > +static void __init build_sched_topology(void)
 > > +{
 > >      /*
 > > -     * There must be one trailing NULL entry left.
 > > +     * When there is NUMA topology inside the package invalidate the
 > > +     * PKG domain since the NUMA domains will auto-magically create the
 > > +     * right spanning domains based on the SLIT.
 > >       */
 > > -    BUG_ON(i >= ARRAY_SIZE(x86_topology)-1);
 > > +    if (x86_has_numa_in_package) {
 > > +        unsigned int pkgdom = ARRAY_SIZE(x86_topology) - 2;
 > >  
 > > +        memset(&x86_topology[pkgdom], 0, sizeof(x86_topology[pkgdom]));
 > > +    }
 > >      set_sched_topology(x86_topology);
 > >  }
 > 
 > Urgh, this patch is doing at least 4 things and nigh on unreadable
 > because of that.
 > 
 >  - introduces DOMAIN() helper
 >  - drops (the now pointless) SD_INIT_NAME() helper
 >  - drops CONFIG_SCHED_SMT (x86 special)
 >  - moves to static initialize and truncate

Thanks for your review, I would split this Thomas's patch to 4 different patches
and preserve his signoff