From 1b08782ce31f612d98e11ccccf3e3df9a147a67d Mon Sep 17 00:00:00 2001 From: Dietmar Eggemann Date: Tue, 22 Sep 2020 10:39:34 +0200 Subject: sched/cpupri: Remove pri_to_cpu[1] pri_to_cpu[1] isn't used since cpupri_set(..., newpri) is never called with newpri = 99. The valid RT priorities RT1..RT99 (p->rt_priority = [1..99]) map into cpupri (idx of pri_to_cpu[]) = [2..100] Current 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 So cpupri = 1 isn't used. Reduce the size of pri_to_cpu[] by 1 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 1 ... 49 50 50 49 50 49 49 50 ... 99 0 0 99 Signed-off-by: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200922083934.19275-3-dietmar.eggemann@arm.com --- kernel/sched/cpupri.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/sched/cpupri.c') diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c index a5d14ed485f4..8d9952a51664 100644 --- a/kernel/sched/cpupri.c +++ b/kernel/sched/cpupri.c @@ -19,12 +19,12 @@ * 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(101, nr_domcpus)), though the scenario that + * worst case complexity of O(min(100, 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 101 based cpupri */ +/* Convert between a 140 based task->prio, and our 100 based cpupri */ static int convert_prio(int prio) { int cpupri; @@ -34,7 +34,7 @@ static int convert_prio(int prio) else if (prio >= MAX_RT_PRIO) cpupri = CPUPRI_NORMAL; else - cpupri = MAX_RT_PRIO - prio; + cpupri = MAX_RT_PRIO - prio - 1; return cpupri; } -- cgit v1.2.3