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McKenney" , "Gautham R. Shenoy" , Florian Weimer , Tim Chen , Shrikanth Hegde Subject: Re: [patch V4 08/20] sched/mmcid: Use cpumask_weighted_or() Message-ID: References: <20251104075053.700034556@linutronix.de> <20251104075427.153226202@linutronix.de> 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: <20251104075427.153226202@linutronix.de> On Sun, Nov 16, 2025 at 09:48:49PM +0100, Thomas Gleixner wrote: > Use cpumask_weighted_or() instead of cpumask_or() and cpumask_weight() on > the result, which walks the same bitmap twice. Results in 10-20% less > cycles, which reduces the runqueue lock hold time. > > Signed-off-by: Thomas Gleixner > Reviewed-by: Mathieu Desnoyers Acked-by: Yury Norov (NVIDIA) > --- > kernel/sched/core.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -10377,6 +10377,7 @@ void call_trace_sched_update_nr_running( > static inline void mm_update_cpus_allowed(struct mm_struct *mm, const struct cpumask *affmsk) > { > struct cpumask *mm_allowed; > + unsigned int weight; > > if (!mm) > return; > @@ -10387,8 +10388,8 @@ static inline void mm_update_cpus_allowe > */ > guard(raw_spinlock)(&mm->mm_cid.lock); > mm_allowed = mm_cpus_allowed(mm); > - cpumask_or(mm_allowed, mm_allowed, affmsk); > - WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, cpumask_weight(mm_allowed)); > + weight = cpumask_weighted_or(mm_allowed, mm_allowed, affmsk); > + WRITE_ONCE(mm->mm_cid.nr_cpus_allowed, weight); > } > > void sched_mm_cid_exit_signals(struct task_struct *t)