Messages in this thread Patch in this message | | | Date | Wed, 30 May 2018 16:22:37 +0200 | From | Peter Zijlstra <> | Subject | [RFC 01/11] sched/fair: Fix select_idle_cpu()s cost accounting |
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We compute the average cost of the total scan, but then use it as a per-cpu scan cost when computing the scan proportion. Fix this by properly computing a per-cpu scan cost.
This also fixes a bug where we would terminate early (!--nr, case) and not account that cost at all.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/sched/fair.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6368,11 +6368,11 @@ static inline int select_idle_smt(struct */ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target) { + int cpu, loops = 0, nr = INT_MAX; struct sched_domain *this_sd; u64 avg_cost, avg_idle; u64 time, cost; s64 delta; - int cpu, nr = INT_MAX; this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc)); if (!this_sd) @@ -6399,8 +6399,10 @@ static int select_idle_cpu(struct task_s time = local_clock(); for_each_cpu_wrap(cpu, sched_domain_span(sd), target) { - if (!--nr) - return -1; + if (loops++ >= nr) { + cpu = -1; + break; + } if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) continue; if (available_idle_cpu(cpu)) @@ -6408,6 +6410,7 @@ static int select_idle_cpu(struct task_s } time = local_clock() - time; + time = div_u64(time, loops); cost = this_sd->avg_scan_cost; delta = (s64)(time - cost) / 8; this_sd->avg_scan_cost += delta;
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