From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 213A83D5C0B for ; Tue, 12 May 2026 16:57:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778605054; cv=none; b=E6A8Jdx5Gr+yxRFGOzTYViH9Ld4Wg5Iu1xdEnIC8dzkS6h0XMg6t+ngGEVBMIfhGqk0D0ClNDSF0Z0+l7/ESHdJhy7z1neoYjFLmmO9myxQdBhXFB6QXSg9t8LfA/6bDRWr33L+SJ9EnpTsjd/wGmS+MiisfxUbBEJquJQqGU2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778605054; c=relaxed/simple; bh=M6guOYyn8S4/48NE1gQKbvpMb0qqOc0AhDb4o1iAa0Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=guyuebuVAQZmqA3LgVFB8ASF69w7AEA+wCdJt3ZnwrRzeifpW3GLWKiDGSXsbRmEt7DJQPa8dsnVPJFICdzPU4S7mEFh5Nqh9/Hbm+DTViU3MAjymHBgRcoC9h0HkqylOEiqZt6ijFcj9Bq7CLPV17fqGQTlBnkvvdEYlK5Bvmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=AF3ODMS3; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="AF3ODMS3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1778605052; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=EwnliE8D1utEezY/QOXZIrCxb9uUWMUiQOjNCIEfFdk=; b=AF3ODMS3gtj9NKSTTlAsakjxPNIAZCuzzwMRLy/yW80NI4cIQVKcSTiiVK6o3RQ2Urd/fb W7mMfpsoJWhvOHUji6r4QVoIUF7SNE1xGcJP39WcOZEPrH//WUnJiMfUxnxp+A+Y/1XjbO padnZJ5x6FawpzEUjnZB31/lHdWXb7Q= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-477-OK39eR62NrKA0l7nu_EyWA-1; Tue, 12 May 2026 12:57:28 -0400 X-MC-Unique: OK39eR62NrKA0l7nu_EyWA-1 X-Mimecast-MFC-AGG-ID: OK39eR62NrKA0l7nu_EyWA_1778605046 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 72EFF1800372; Tue, 12 May 2026 16:57:26 +0000 (UTC) Received: from pauld.westford.csb (headnet01.pony-001.prod.iad2.dc.redhat.com [10.2.32.101]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E9C7A30001BE; Tue, 12 May 2026 16:57:23 +0000 (UTC) Date: Tue, 12 May 2026 12:57:21 -0400 From: Phil Auld To: Shrikanth Hegde Cc: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com, juri.lelli@redhat.com, vschneid@redhat.com, dietmar.eggemann@arm.com, tj@kernel.org, rostedt@goodmis.org, mgorman@suse.de, bsegall@google.com, arighi@nvidia.com Subject: Re: [PATCH v2 2/3] sched: Simplify ifdeffery around cpu_smt_mask Message-ID: <20260512165721.GC140541@pauld.westford.csb> References: <20260512152125.308280-1-sshegde@linux.ibm.com> <20260512152125.308280-3-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260512152125.308280-3-sshegde@linux.ibm.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Tue, May 12, 2026 at 08:51:24PM +0530 Shrikanth Hegde wrote: > Now, that cpu_smt_mask is defined as cpumask_of(cpu) for > CONFIG_SCHED_SMT=n, it is possible to get rid of the ifdeffery. > > Effectively, > - This makes sched_smt_present is defined always > > - cpumask_weight(cpumask_of(cpu)) == 1. So sched_smt_present_inc/dec > will never enable the sched_smt_present. Which is expected. > > - Paths that were compile-time eliminated become runtime guarded > using static keys. > > - Defines set_idle_cores, test_idle_cores etc which could likely benefit > the CONFIG_SCHED_SMT=n systems to use the same optimizations within the > LLC at wakeups. > > - This will expose sched_smt_present symbol for CONFIG_SCHED_SMT=n. > Likely not a concern. > > - There a bloat of code CONFIG_SCHED_SMT=n. (NR_CPUS=2048) > add/remove: 24/18 grow/shrink: 26/28 up/down: 6396/-3188 (3208) > Total: Before=30629880, After=30633088, chg +0.01% > > - No code bloat for CONFIG_SCHED_SMT=y, which is expected. > > - Add comments around stop_core_cpuslocked on why ifdefs are not > removed. > > - This leaves the remaining uses of CONFIG_SCHED_SMT mainly for > topology building bits which have a policy based decision. > > Acked-by: Tejun Heo > Signed-off-by: Shrikanth Hegde LGTM. Reviewed-by: Phil Auld Cheers, Phil > --- > include/linux/sched/smt.h | 4 ---- > kernel/sched/core.c | 6 ------ > kernel/sched/ext_idle.c | 6 ------ > kernel/sched/fair.c | 35 ----------------------------------- > kernel/sched/sched.h | 6 ------ > kernel/sched/topology.c | 2 -- > kernel/stop_machine.c | 5 +++++ > kernel/workqueue.c | 4 ---- > 8 files changed, 5 insertions(+), 63 deletions(-) > > diff --git a/include/linux/sched/smt.h b/include/linux/sched/smt.h > index 166b19af956f..cde6679c0278 100644 > --- a/include/linux/sched/smt.h > +++ b/include/linux/sched/smt.h > @@ -4,16 +4,12 @@ > > #include > > -#ifdef CONFIG_SCHED_SMT > extern struct static_key_false sched_smt_present; > > static __always_inline bool sched_smt_active(void) > { > return static_branch_likely(&sched_smt_present); > } > -#else > -static __always_inline bool sched_smt_active(void) { return false; } > -#endif > > void arch_smt_update(void); > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b905805bbcbe..3ae5f19c1b7e 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -8612,18 +8612,14 @@ static void cpuset_cpu_inactive(unsigned int cpu) > > static inline void sched_smt_present_inc(int cpu) > { > -#ifdef CONFIG_SCHED_SMT > if (cpumask_weight(cpu_smt_mask(cpu)) == 2) > static_branch_inc_cpuslocked(&sched_smt_present); > -#endif > } > > static inline void sched_smt_present_dec(int cpu) > { > -#ifdef CONFIG_SCHED_SMT > if (cpumask_weight(cpu_smt_mask(cpu)) == 2) > static_branch_dec_cpuslocked(&sched_smt_present); > -#endif > } > > int sched_cpu_activate(unsigned int cpu) > @@ -8711,9 +8707,7 @@ int sched_cpu_deactivate(unsigned int cpu) > */ > sched_smt_present_dec(cpu); > > -#ifdef CONFIG_SCHED_SMT > sched_core_cpu_deactivate(cpu); > -#endif > > if (!sched_smp_initialized) > return 0; > diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c > index 6e1980763270..9f5ad6b071f9 100644 > --- a/kernel/sched/ext_idle.c > +++ b/kernel/sched/ext_idle.c > @@ -79,7 +79,6 @@ static bool scx_idle_test_and_clear_cpu(int cpu) > int node = scx_cpu_node_if_enabled(cpu); > struct cpumask *idle_cpus = idle_cpumask(node)->cpu; > > -#ifdef CONFIG_SCHED_SMT > /* > * SMT mask should be cleared whether we can claim @cpu or not. The SMT > * cluster is not wholly idle either way. This also prevents > @@ -104,7 +103,6 @@ static bool scx_idle_test_and_clear_cpu(int cpu) > else if (cpumask_test_cpu(cpu, idle_smts)) > __cpumask_clear_cpu(cpu, idle_smts); > } > -#endif > > return cpumask_test_and_clear_cpu(cpu, idle_cpus); > } > @@ -622,7 +620,6 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, > goto out_unlock; > } > > -#ifdef CONFIG_SCHED_SMT > /* > * Use @prev_cpu's sibling if it's idle. > */ > @@ -634,7 +631,6 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, > goto out_unlock; > } > } > -#endif > > /* > * Search for any idle CPU in the same LLC domain. > @@ -714,7 +710,6 @@ static void update_builtin_idle(int cpu, bool idle) > > assign_cpu(cpu, idle_cpus, idle); > > -#ifdef CONFIG_SCHED_SMT > if (sched_smt_active()) { > const struct cpumask *smt = cpu_smt_mask(cpu); > struct cpumask *idle_smts = idle_cpumask(node)->smt; > @@ -731,7 +726,6 @@ static void update_builtin_idle(int cpu, bool idle) > cpumask_andnot(idle_smts, idle_smts, smt); > } > } > -#endif > } > > /* > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 3ebec186f982..353e31ecaadc 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1584,7 +1584,6 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se) > > static inline bool is_core_idle(int cpu) > { > -#ifdef CONFIG_SCHED_SMT > int sibling; > > for_each_cpu(sibling, cpu_smt_mask(cpu)) { > @@ -1594,7 +1593,6 @@ static inline bool is_core_idle(int cpu) > if (!idle_cpu(sibling)) > return false; > } > -#endif > > return true; > } > @@ -2277,7 +2275,6 @@ numa_type numa_classify(unsigned int imbalance_pct, > return node_fully_busy; > } > > -#ifdef CONFIG_SCHED_SMT > /* Forward declarations of select_idle_sibling helpers */ > static inline bool test_idle_cores(int cpu); > static inline int numa_idle_core(int idle_core, int cpu) > @@ -2295,12 +2292,6 @@ static inline int numa_idle_core(int idle_core, int cpu) > > return idle_core; > } > -#else /* !CONFIG_SCHED_SMT: */ > -static inline int numa_idle_core(int idle_core, int cpu) > -{ > - return idle_core; > -} > -#endif /* !CONFIG_SCHED_SMT */ > > /* > * Gather all necessary information to make NUMA balancing placement > @@ -7811,7 +7802,6 @@ static inline int __select_idle_cpu(int cpu, struct task_struct *p) > return -1; > } > > -#ifdef CONFIG_SCHED_SMT > DEFINE_STATIC_KEY_FALSE(sched_smt_present); > EXPORT_SYMBOL_GPL(sched_smt_present); > > @@ -7921,29 +7911,6 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t > return -1; > } > > -#else /* !CONFIG_SCHED_SMT: */ > - > -static inline void set_idle_cores(int cpu, int val) > -{ > -} > - > -static inline bool test_idle_cores(int cpu) > -{ > - return false; > -} > - > -static inline int select_idle_core(struct task_struct *p, int core, struct cpumask *cpus, int *idle_cpu) > -{ > - return __select_idle_cpu(core, p); > -} > - > -static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) > -{ > - return -1; > -} > - > -#endif /* !CONFIG_SCHED_SMT */ > - > /* > * Scan the LLC domain for idle CPUs; this is dynamically regulated by > * comparing the average scan cost (tracked in sd->avg_scan_cost) against the > @@ -12036,9 +12003,7 @@ static int should_we_balance(struct lb_env *env) > * idle has been found, then its not needed to check other > * SMT siblings for idleness: > */ > -#ifdef CONFIG_SCHED_SMT > cpumask_andnot(swb_cpus, swb_cpus, cpu_smt_mask(cpu)); > -#endif > continue; > } > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 9f63b15d309d..e476623a0c2a 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1667,7 +1667,6 @@ do { \ > flags = _raw_spin_rq_lock_irqsave(rq); \ > } while (0) > > -#ifdef CONFIG_SCHED_SMT > extern void __update_idle_core(struct rq *rq); > > static inline void update_idle_core(struct rq *rq) > @@ -1676,12 +1675,7 @@ static inline void update_idle_core(struct rq *rq) > __update_idle_core(rq); > } > > -#else /* !CONFIG_SCHED_SMT: */ > -static inline void update_idle_core(struct rq *rq) { } > -#endif /* !CONFIG_SCHED_SMT */ > - > #ifdef CONFIG_FAIR_GROUP_SCHED > - > static inline struct task_struct *task_of(struct sched_entity *se) > { > WARN_ON_ONCE(!entity_is_task(se)); > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 5847b83d9d55..a1f46e3f4ede 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -1310,9 +1310,7 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd) > cpumask_copy(mask, sched_group_span(sg)); > for_each_cpu(cpu, mask) { > cores++; > -#ifdef CONFIG_SCHED_SMT > cpumask_andnot(mask, mask, cpu_smt_mask(cpu)); > -#endif > } > sg->cores = cores; > > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c > index 3fe6b0c99f3d..773d8e9ae30c 100644 > --- a/kernel/stop_machine.c > +++ b/kernel/stop_machine.c > @@ -633,6 +633,11 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus) > EXPORT_SYMBOL_GPL(stop_machine); > > #ifdef CONFIG_SCHED_SMT > +/* > + * INTEL_IFS is the only user of this API. That selftest can > + * only be compiled if SMP=y. On x86 it selects SCHED_SMT. > + * Keep the ifdefs for now. > + */ > int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data) > { > const struct cpumask *smt_mask = cpu_smt_mask(cpu); > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 3d2e3b2ec528..c911fdcb4428 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -8198,11 +8198,7 @@ static bool __init cpus_dont_share(int cpu0, int cpu1) > > static bool __init cpus_share_smt(int cpu0, int cpu1) > { > -#ifdef CONFIG_SCHED_SMT > return cpumask_test_cpu(cpu0, cpu_smt_mask(cpu1)); > -#else > - return false; > -#endif > } > > static bool __init cpus_share_numa(int cpu0, int cpu1) > -- > 2.47.3 > > --