diff options
| author | Ricardo Neri <ricardo.neri-calderon@linux.intel.com> | 2023-07-07 15:57:03 -0700 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-07-13 15:21:52 +0200 |
| commit | b1bfeab9b00283f521d2100afb9f5af84ccdae13 (patch) | |
| tree | 574e3a022ce5064e431c38a4cde6514bec9ff5b1 /kernel/sched | |
| parent | 7ff1693236f5d97a939dbeb660c07671a2d57071 (diff) | |
| download | linux-b1bfeab9b00283f521d2100afb9f5af84ccdae13.tar.gz | |
sched/fair: Consider the idle state of the whole core for load balance
should_we_balance() traverses the group_balance_mask (AND'ed with lb_env::
cpus) starting from lower numbered CPUs looking for the first idle CPU.
In hybrid x86 systems, the siblings of SMT cores get CPU numbers, before
non-SMT cores:
[0, 1] [2, 3] [4, 5] 6 7 8 9
b i b i b i b i i i
In the figure above, CPUs in brackets are siblings of an SMT core. The
rest are non-SMT cores. 'b' indicates a busy CPU, 'i' indicates an
idle CPU.
We should let a CPU on a fully idle core get the first chance to idle
load balance as it has more CPU capacity than a CPU on an idle SMT
CPU with busy sibling. So for the figure above, if we are running
should_we_balance() to CPU 1, we should return false to let CPU 7 on
idle core to have a chance first to idle load balance.
A partially busy (i.e., of type group_has_spare) local group with SMT
cores will often have only one SMT sibling busy. If the destination CPU
is a non-SMT core, partially busy, lower-numbered, SMT cores should not
be considered when finding the first idle CPU.
However, in should_we_balance(), when we encounter idle SMT first in partially
busy core, we prematurely break the search for the first idle CPU.
Higher-numbered, non-SMT cores is not given the chance to have
idle balance done on their behalf. Those CPUs will only be considered
for idle balancing by chance via CPU_NEWLY_IDLE.
Instead, consider the idle state of the whole SMT core.
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/807bdd05331378ea3bf5956bda87ded1036ba769.1688770494.git.tim.c.chen@linux.intel.com
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/fair.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c6246fbcd74f48..a87988327f889c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10902,7 +10902,7 @@ static int active_load_balance_cpu_stop(void *data); static int should_we_balance(struct lb_env *env) { struct sched_group *sg = env->sd->groups; - int cpu; + int cpu, idle_smt = -1; /* * Ensure the balancing environment is consistent; can happen @@ -10929,10 +10929,24 @@ static int should_we_balance(struct lb_env *env) if (!idle_cpu(cpu)) continue; + /* + * Don't balance to idle SMT in busy core right away when + * balancing cores, but remember the first idle SMT CPU for + * later consideration. Find CPU on an idle core first. + */ + if (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && !is_core_idle(cpu)) { + if (idle_smt == -1) + idle_smt = cpu; + continue; + } + /* Are we the first idle CPU? */ return cpu == env->dst_cpu; } + if (idle_smt == env->dst_cpu) + return true; + /* Are we the first CPU of this group ? */ return group_balance_cpu(sg) == env->dst_cpu; } |