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Tue, 03 Nov 2026 18:09:59 -0800 (PST) Received: from osman.mioffice.cn ([43.224.245.178]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1b245c6f0dcsm3560432c88.21.2026.11.03.18.09.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 18:09:59 -0800 (PST) From: Zhan Xusheng To: peterz@infradead.org, mingo@kernel.org Cc: tim.c.chen@linux.intel.com, qyousef@layalina.io, yu.c.chen@intel.com, vincent.guittot@linaro.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, zhanxusheng@xiaomi.com Subject: [PATCH v2] sched/cache: Don't use fits_capacity() to compare thread and CPU counts Date: Wed, 4 Nov 2026 10:09:54 +0800 Message-ID: <20261104020954.2388172-1-zhanxusheng1024@gmail.com> X-Mailer: git-send-email 2.43.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Zhan Xusheng invalid_llc_nr() checks that a process's running threads stay below 80% of the LLC's cores, scaled by llc_aggr_tolerance, with fits_capacity(). fits_capacity() is meant for capacity values; here it only supplies the 20% margin. Give the check its own helper. x * 5 < y * 4 is the same comparison as x * 1280 < y * 1024, so there is no functional change. Signed-off-by: Zhan Xusheng Reviewed-by: Tim Chen Reviewed-by: Qais Yousef --- Qais's series changes fits_capacity() to take a CPU number as its second argument [1]; this call would then pass the CPU count as a CPU number without a warning. v2: reword the comment (Tim); move the reason above out of the changelog; add the Reviewed-by tags. v1: https://lore.kernel.org/all/20261102021536.1026143-1-zhanxusheng1024@gmail.com/ [1] https://lore.kernel.org/all/20260504020003.71306-5-qyousef@layalina.io/ kernel/sched/fair.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index cfc982205b98..a7467fe425e6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1469,6 +1469,12 @@ static bool exceed_llc_capacity(struct sched_cache_group *grp, int cpu) return false; } +/* Number of running threads below 80% of LLC's cores for default setting */ +static inline bool fits_llc_nr(u64 nr_threads, unsigned int nr_cpus) +{ + return nr_threads * 5 < (u64)nr_cpus * 4; +} + static bool invalid_llc_nr(struct sched_cache_group *grp, struct task_struct *p, int cpu) { @@ -1485,8 +1491,8 @@ static bool invalid_llc_nr(struct sched_cache_group *grp, struct task_struct *p, if (scale == INT_MAX) return false; - return !fits_capacity((READ_ONCE(grp->nr_running_avg) * cpu_smt_num_threads), - (scale * per_cpu(sd_llc_size, cpu))); + return !fits_llc_nr(READ_ONCE(grp->nr_running_avg) * cpu_smt_num_threads, + scale * per_cpu(sd_llc_size, cpu)); } /* -- 2.43.0