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[86.163.217.97]) by smtp.gmail.com with ESMTPSA id m13-20020a7bce0d000000b003fbaa2903f4sm671285wmc.19.2023.07.17.14.57.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Jul 2023 14:57:33 -0700 (PDT) From: Qais Yousef To: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann Cc: linux-kernel@vger.kernel.org, Lukasz Luba , Wei Wang , Xuewen Yan , Hank , Jonathan JMChen , Hongyan Xia , Qais Yousef Subject: [PATCH v3 1/3] sched/uclamp: Set max_spare_cap_cpu even if max_spare_cap is 0 Date: Mon, 17 Jul 2023 22:57:15 +0100 Message-Id: <20230717215717.309174-2-qyousef@layalina.io> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230717215717.309174-1-qyousef@layalina.io> References: <20230717215717.309174-1-qyousef@layalina.io> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" When uclamp_max is being used, the util of the task could be higher than the spare capacity of the CPU, but due to uclamp_max value we force fit it there. The way the condition for checking for max_spare_cap in find_energy_efficient_cpu() was constructed; it ignored any CPU that has its spare_cap less than or _equal_ to max_spare_cap. Since we initialize max_spare_cap to 0; this lead to never setting max_spare_cap_cpu and hence ending up never performing compute_energy() for this cluster and missing an opportunity for a better energy efficient placement to honour uclamp_max setting. max_spare_cap =3D 0; cpu_cap =3D capacity_of(cpu) - task_util(p); // 0 if task_util(p) is high ... util_fits_cpu(...); // will return true if uclamp_max forces it to fit ... // this logic will fail to update max_spare_cap_cpu if cpu_cap is 0 if (cpu_cap > max_spare_cap) { max_spare_cap =3D cpu_cap; max_spare_cap_cpu =3D cpu; } prev_spare_cap suffers from a similar problem. Fix the logic by converting the variables into long and treating -1 value as 'not populated' instead of 0 which is a viable and correct spare capacity value. We need to be careful signed comparison is used when comparing with cpu_cap in one of the conditions. Fixes: 1d42509e475c ("sched/fair: Make EAS wakeup placement consider uclamp= restrictions") Signed-off-by: Qais Yousef (Google) Reviewed-by: Vincent Guittot --- kernel/sched/fair.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0cd1cdbae534..d489eece5a0d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7596,11 +7596,10 @@ static int find_energy_efficient_cpu(struct task_st= ruct *p, int prev_cpu) for (; pd; pd =3D pd->next) { unsigned long util_min =3D p_util_min, util_max =3D p_util_max; unsigned long cpu_cap, cpu_thermal_cap, util; - unsigned long cur_delta, max_spare_cap =3D 0; + long prev_spare_cap =3D -1, max_spare_cap =3D -1; unsigned long rq_util_min, rq_util_max; - unsigned long prev_spare_cap =3D 0; + unsigned long cur_delta, base_energy; int max_spare_cap_cpu =3D -1; - unsigned long base_energy; int fits, max_fits =3D -1; =20 cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask); @@ -7663,7 +7662,7 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) prev_spare_cap =3D cpu_cap; prev_fits =3D fits; } else if ((fits > max_fits) || - ((fits =3D=3D max_fits) && (cpu_cap > max_spare_cap))) { + ((fits =3D=3D max_fits) && ((long)cpu_cap > max_spare_cap))) { /* * Find the CPU with the maximum spare capacity * among the remaining CPUs in the performance @@ -7675,7 +7674,7 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) } } =20 - if (max_spare_cap_cpu < 0 && prev_spare_cap =3D=3D 0) + if (max_spare_cap_cpu < 0 && prev_spare_cap < 0) continue; =20 eenv_pd_busy_time(&eenv, cpus, p); @@ -7683,7 +7682,7 @@ static int find_energy_efficient_cpu(struct task_stru= ct *p, int prev_cpu) base_energy =3D compute_energy(&eenv, pd, cpus, p, -1); =20 /* Evaluate the energy impact of using prev_cpu. */ - if (prev_spare_cap > 0) { + if (prev_spare_cap > -1) { prev_delta =3D compute_energy(&eenv, pd, cpus, p, prev_cpu); /* CPU utilization has changed */ --=20 2.25.1