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Sun, 01 Nov 2026 18:15:43 -0800 (PST) Received: from osman.mioffice.cn ([43.224.245.178]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae845429e6sm11721288a91.6.2026.11.01.18.15.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Nov 2026 18:15:42 -0800 (PST) From: Zhan Xusheng To: peterz@infradead.org, mingo@kernel.org Cc: qyousef@layalina.io, tim.c.chen@linux.intel.com, 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] sched/cache: Don't use fits_capacity() to compare thread and CPU counts Date: Mon, 2 Nov 2026 10:15:36 +0800 Message-ID: <20261102021536.1026143-1-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() uses fits_capacity() to compare a thread count with a CPU count, only for its 20% margin. Qais's series changes fits_capacity() to take a CPU number as its second argument, and this call would then pass the CPU count as a CPU number without a warning. 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. Link: https://lore.kernel.org/all/20260504020003.71306-5-qyousef@layalina.io/ Signed-off-by: Zhan Xusheng --- This keeps the 20% margin. Qais would rather not add hardcoded margins, and llc_aggr_tolerance already scales the LLC size here, so the margin could go, but that changes when a process stops being aggregated. Tim, Chen Yu, would you drop it? 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..dfd6528d18ee 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; } +/* Are the running threads (in SMT siblings) below ~80% of the LLC's CPUs? */ +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)); } /* base-commit: c339f4010dea8b0d754f84ace70cd1b089878ef8 -- 2.43.0