From 5e054bca44fe92323de5e9b71478d1904b8bb1b7 Mon Sep 17 00:00:00 2001 From: Dietmar Eggemann Date: Tue, 22 Sep 2020 10:39:33 +0200 Subject: [PATCH] sched/cpupri: Remove pri_to_cpu[CPUPRI_IDLE] pri_to_cpu[CPUPRI_IDLE=0] isn't used since cpupri_set(..., newpri) is never called with newpri = MAX_PRIO (140). Current mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 140 0 (CPUPRI_IDLE) 100 1 (CPUPRI_NORMAL) 1 98 98 3 ... 49 50 50 51 50 49 49 52 ... 99 0 0 101 Even when cpupri was introduced with commit 6e0534f27819 ("sched: use a 2-d bitmap for searching lowest-pri CPU") in v2.6.27, only (1) CPUPRI_INVALID (-1), (2) MAX_RT_PRIO (100), (3) an RT prio (RT1..RT99) were used as newprio in cpupri_set(..., newpri) -> convert_prio(newpri). MAX_RT_PRIO is used only in dec_rt_tasks() -> dec_rt_prio() -> dec_rt_prio_smp() -> cpupri_set() in case of !rt_rq->rt_nr_running. I.e. it stands for a non-rt task, including the IDLE task. Commit 57785df5ac53 ("sched: Fix task priority bug") removed code in v2.6.33 which did set the priority of the IDLE task to MAX_PRIO. Although this happened after the introduction of cpupri, it didn't have an effect on the values used for cpupri_set(..., newpri). Remove CPUPRI_IDLE and adapt the cpupri implementation accordingly. This will save a useless for loop with an atomic_read in cpupri_find_fitness() calling __cpupri_find(). New mapping: p->rt_priority p->prio newpri cpupri -1 -1 (CPUPRI_INVALID) 100 0 (CPUPRI_NORMAL) 1 98 98 2 ... 49 50 50 50 50 49 49 51 ... 99 0 0 100 Signed-off-by: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200922083934.19275-2-dietmar.eggemann@arm.com --- kernel/sched/cpupri.c | 10 ++++------ kernel/sched/cpupri.h | 7 +++---- 2 files changed, 7 insertions(+), 10 deletions(-) diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c index 0033731..a5d14ed 100644 --- a/kernel/sched/cpupri.c +++ b/kernel/sched/cpupri.c @@ -11,7 +11,7 @@ * This code tracks the priority of each CPU so that global migration * decisions are easy to calculate. Each CPU can be in a state as follows: * - * (INVALID), IDLE, NORMAL, RT1, ... RT99 + * (INVALID), NORMAL, RT1, ... RT99 * * going from the lowest priority to the highest. CPUs in the INVALID state * are not eligible for routing. The system maintains this state with @@ -19,24 +19,22 @@ * in that class). Therefore a typical application without affinity * restrictions can find a suitable CPU with O(1) complexity (e.g. two bit * searches). For tasks with affinity restrictions, the algorithm has a - * worst case complexity of O(min(102, nr_domcpus)), though the scenario that + * worst case complexity of O(min(101, nr_domcpus)), though the scenario that * yields the worst case search is fairly contrived. */ #include "sched.h" -/* Convert between a 140 based task->prio, and our 102 based cpupri */ +/* Convert between a 140 based task->prio, and our 101 based cpupri */ static int convert_prio(int prio) { int cpupri; if (prio == CPUPRI_INVALID) cpupri = CPUPRI_INVALID; - else if (prio == MAX_PRIO) - cpupri = CPUPRI_IDLE; else if (prio >= MAX_RT_PRIO) cpupri = CPUPRI_NORMAL; else - cpupri = MAX_RT_PRIO - prio + 1; + cpupri = MAX_RT_PRIO - prio; return cpupri; } diff --git a/kernel/sched/cpupri.h b/kernel/sched/cpupri.h index efbb492..1a16236 100644 --- a/kernel/sched/cpupri.h +++ b/kernel/sched/cpupri.h @@ -1,11 +1,10 @@ /* SPDX-License-Identifier: GPL-2.0 */ -#define CPUPRI_NR_PRIORITIES (MAX_RT_PRIO + 2) +#define CPUPRI_NR_PRIORITIES (MAX_RT_PRIO + 1) #define CPUPRI_INVALID -1 -#define CPUPRI_IDLE 0 -#define CPUPRI_NORMAL 1 -/* values 2-101 are RT priorities 0-99 */ +#define CPUPRI_NORMAL 0 +/* values 2-100 are RT priorities 0-99 */ struct cpupri_vec { atomic_t count; -- 2.7.4