Messages in this thread Patch in this message | | | From | Ricardo Neri <> | Subject | [PATCH v3 20/24] sched/fair: Introduce sched_smt_siblings_idle() | Date | Mon, 6 Feb 2023 21:11:01 -0800 |
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X86 needs to know the idle state of the SMT siblings of a CPU to improve the accuracy of IPCC classification. X86 implements support for IPC classes in the thermal HFI driver.
Rename is_core_idle() as sched_smt_siblings_idle() and make it available outside the scheduler code.
Cc: Ben Segall <bsegall@google.com> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Len Brown <len.brown@intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Tim C. Chen <tim.c.chen@intel.com> Cc: Valentin Schneider <vschneid@redhat.com> Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> --- is_core_idle() is no longer an inline function after this patch. To rule out performance degradation, I compared the execution time of the inline and non-inline versions on a 4-socket Cascade Lake system using the NUMA stressor of stress-ng:
$ stress-ng --numa 1500 -t 10m
is_core_idle() was called ~200,000 times. I measured the value of the TSC counter before and after calling is_core_idle() and computed the delta value.
I arbitrarily removed outliers (defined as any delta larger than 5000 counts). This required removing ~40 samples.
The table below summarizes the difference in execution time. All quantities are expressed in TSC counts, except the standard deviation, expressed as a percentage of the average.
Average Median Std(%) Mode TSCdelta inline 668.76 626 67.24 42 TSCdelta non-inline 677.64 624 67.67 46
All metrics are similar for the inline and non-inline cases. --- Changes since v2: * Brought back this previously dropped patch. * Profiled inline vs non-inline is_core_idle(). I found not major penalty. * Merged is_core_idle() and sched_smt_siblings_idle() into a single function. (Dietmar)
Changes since v1: * Dropped this patch. --- include/linux/sched.h | 2 ++ kernel/sched/fair.c | 21 +++++++++++++++------ 2 files changed, 17 insertions(+), 6 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index 45f28a601b3d..7ef9fd84e7ad 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2449,4 +2449,6 @@ static inline void sched_core_fork(struct task_struct *p) { } extern void sched_set_stop_task(int cpu, struct task_struct *stop); +extern bool sched_smt_siblings_idle(int cpu); + #endif diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d3c22dc145f7..a66d86c5cb5c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1064,7 +1064,14 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se) * Scheduling class queueing methods: */ -static inline bool is_core_idle(int cpu) +/** + * sched_smt_siblings_idle - Check whether SMT siblings of a CPU are idle + * @cpu: The CPU to check + * + * Returns true if all the SMT siblings of @cpu are idle or @cpu does not have + * SMT siblings. The idle state of @cpu is not considered. + */ +bool sched_smt_siblings_idle(int cpu) { #ifdef CONFIG_SCHED_SMT int sibling; @@ -1767,7 +1774,7 @@ static inline int numa_idle_core(int idle_core, int cpu) * Prefer cores instead of packing HT siblings * and triggering future load balancing. */ - if (is_core_idle(cpu)) + if (sched_smt_siblings_idle(cpu)) idle_core = cpu; return idle_core; @@ -9518,7 +9525,8 @@ sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs * If the destination CPU has SMT siblings, env->idle != CPU_NOT_IDLE * is not sufficient. We need to make sure the whole core is idle. */ - if (sds->local->flags & SD_SHARE_CPUCAPACITY && !is_core_idle(env->dst_cpu)) + if (sds->local->flags & SD_SHARE_CPUCAPACITY && + !sched_smt_siblings_idle(env->dst_cpu)) return false; /* Only do SMT checks if either local or candidate have SMT siblings. */ @@ -10687,7 +10695,8 @@ static struct rq *find_busiest_queue(struct lb_env *env, sched_asym_prefer(i, env->dst_cpu) && nr_running == 1) { if (env->sd->flags & SD_SHARE_CPUCAPACITY || - (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && is_core_idle(i))) + (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && + sched_smt_siblings_idle(i))) continue; } @@ -10816,7 +10825,7 @@ asym_active_balance(struct lb_env *env) * busy sibling. */ return sched_asym_prefer(env->dst_cpu, env->src_cpu) || - !is_core_idle(env->src_cpu); + !sched_smt_siblings_idle(env->src_cpu); } return false; @@ -11563,7 +11572,7 @@ static void nohz_balancer_kick(struct rq *rq) */ if (sd->flags & SD_SHARE_CPUCAPACITY || (!(sd->flags & SD_SHARE_CPUCAPACITY) && - is_core_idle(i))) { + sched_smt_siblings_idle(i))) { flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; goto unlock; } -- 2.25.1
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