From nobody Mon Feb 9 07:32:47 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 B4A7A345733 for ; Wed, 29 Oct 2025 13:09:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761743356; cv=none; b=BK8Afe9fMPdbIDq7IsAzcUkmMoN6apEU1l6XuWOp3y94VRssoiM62CeCEfw+kDPCuliHjIUbDtaZeTNtUErIL6vVBf82ZYKAPS/z6u9CH2BCuB8sAy5IyDCzquBSk2Ol9eIES02l7dSg4M2C7mRTCDoW1kDOq+/1F2H6iIz+0B0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761743356; c=relaxed/simple; bh=zTGPWweK73AU41i88jsUzIZ9nLv6IzSuopRSgYIM/lg=; h=Message-ID:From:To:Cc:Subject:References:MIME-Version: Content-Type:Date; b=ITmmUO8mHKFQfNK/khYWrIT4MlOCnObka2c65ik2wiH2+7wEb0h7LDrmMaojU4YSB7zLFYOrUqPImGW/iLKPDZ1lvvgWZEiZO7Mw/M3GCtDdeCbQ2sMA99+o3dylgXeVuSTjlG58ZqBUC1v5cqNS9KlBwS0WcBbfJoAVPyCDj6g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=S8ewNkJo; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=CcGrN1Ed; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="S8ewNkJo"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="CcGrN1Ed" Message-ID: <20251029124515.846126176@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1761743351; 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: references:references; bh=//MYkp6W10wSvC2KsqJBKOJnN0+hXB2bifiEHMUus8E=; b=S8ewNkJoDYa7S1IfqtZFIBbf0Ejelewkcll1Kg38hsgsdIUa+InYVKiFpCLsHkcKjBEhOC 6KWnUGSFyHHFWX+SUpCY7NTuJg7sr23lmV1QOIdZyqlB4B/uBkosBzkqMHa1J27ug6OO7r xbm9sOl3Lm+WA/9rYlzPokAFI4PWinSvq4wIG4mDtPDSpEX58XweOuRVug+hfkG/P79smO fT8JouGqkPXwrWc6GxeF2ryCgEWhJMv6igM+Yf0Ay61Jpsf9lhXujohY0TTXMXT6lRqHQR Ff9bUUkWhQ5DAzqN2eeaMKxZ7+N3swoQ/CNrnhqrTKte/AG4AUDgexFR+zmWAg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1761743351; 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: references:references; bh=//MYkp6W10wSvC2KsqJBKOJnN0+hXB2bifiEHMUus8E=; b=CcGrN1EdfiJKm273BA3k6U8nIX/97gEZhvvBQ1+1HQJNZCqDvmUC4TRGyanM8roCsJnttN nffZT2I0ttgHxkCQ== From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Gabriele Monaco , Mathieu Desnoyers , Michael Jeanson , Jens Axboe , "Paul E. McKenney" , "Gautham R. Shenoy" , Florian Weimer , Tim Chen , Yury Norov , Shrikanth Hegde Subject: [patch V3 09/20] cpumask: Cache num_possible_cpus() References: <20251029123717.886619142@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Wed, 29 Oct 2025 14:09:10 +0100 (CET) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Reevaluating num_possible_cpus() over and over does not make sense. That becomes a constant after init as cpu_possible_mask is marked ro_after_init. Cache the value during initialization and provide that for consumption. Signed-off-by: Thomas Gleixner Reviewed-by: Yury Norov Reviewed-by: Shrikanth Hegde --- V2: New patch --- include/linux/cpumask.h | 10 ++++++++-- kernel/cpu.c | 15 +++++++++++++++ 2 files changed, 23 insertions(+), 2 deletions(-) --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -126,6 +126,7 @@ extern struct cpumask __cpu_dying_mask; #define cpu_dying_mask ((const struct cpumask *)&__cpu_dying_mask) =20 extern atomic_t __num_online_cpus; +extern unsigned int __num_possible_cpus; =20 extern cpumask_t cpus_booted_once_mask; =20 @@ -1152,13 +1153,13 @@ void init_cpu_possible(const struct cpum #define __assign_cpu(cpu, mask, val) \ __assign_bit(cpumask_check(cpu), cpumask_bits(mask), (val)) =20 -#define set_cpu_possible(cpu, possible) assign_cpu((cpu), &__cpu_possible_= mask, (possible)) #define set_cpu_enabled(cpu, enabled) assign_cpu((cpu), &__cpu_enabled_mas= k, (enabled)) #define set_cpu_present(cpu, present) assign_cpu((cpu), &__cpu_present_mas= k, (present)) #define set_cpu_active(cpu, active) assign_cpu((cpu), &__cpu_active_mask, = (active)) #define set_cpu_dying(cpu, dying) assign_cpu((cpu), &__cpu_dying_mask, (dy= ing)) =20 void set_cpu_online(unsigned int cpu, bool online); +void set_cpu_possible(unsigned int cpu, bool possible); =20 /** * to_cpumask - convert a NR_CPUS bitmap to a struct cpumask * @@ -1211,7 +1212,12 @@ static __always_inline unsigned int num_ { return raw_atomic_read(&__num_online_cpus); } -#define num_possible_cpus() cpumask_weight(cpu_possible_mask) + +static __always_inline unsigned int num_possible_cpus(void) +{ + return __num_possible_cpus; +} + #define num_enabled_cpus() cpumask_weight(cpu_enabled_mask) #define num_present_cpus() cpumask_weight(cpu_present_mask) #define num_active_cpus() cpumask_weight(cpu_active_mask) --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -3108,6 +3108,9 @@ EXPORT_SYMBOL(__cpu_dying_mask); atomic_t __num_online_cpus __read_mostly; EXPORT_SYMBOL(__num_online_cpus); =20 +unsigned int __num_possible_cpus __ro_after_init =3D NR_CPUS; +EXPORT_SYMBOL(__num_possible_cpus); + void init_cpu_present(const struct cpumask *src) { cpumask_copy(&__cpu_present_mask, src); @@ -3116,6 +3119,7 @@ void init_cpu_present(const struct cpuma void init_cpu_possible(const struct cpumask *src) { cpumask_copy(&__cpu_possible_mask, src); + __num_possible_cpus =3D cpumask_weight(&__cpu_possible_mask); } =20 void set_cpu_online(unsigned int cpu, bool online) @@ -3139,6 +3143,17 @@ void set_cpu_online(unsigned int cpu, bo } } =20 +void set_cpu_possible(unsigned int cpu, bool possible) +{ + if (possible) { + if (!cpumask_test_and_set_cpu(cpu, &__cpu_possible_mask)) + __num_possible_cpus++; + } else { + if (cpumask_test_and_clear_cpu(cpu, &__cpu_possible_mask)) + __num_possible_cpus--; + } +} + /* * Activate the first processor. */