Messages in this thread Patch in this message | | | From | Ricardo Neri <> | Subject | [PATCH v4 20/24] sched/fair: Introduce sched_smt_siblings_idle() | Date | Mon, 12 Jun 2023 21:24:18 -0700 |
| |
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: Perry Yuan <Perry.Yuan@amd.com> 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: Zhao Liu <zhao1.liu@linux.intel.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.
I used this test command:
$ stress-ng --numa 1500 -t 10m
During the test, is_core_idle() was called ~200,000 times. To measure the execution time, I recorded the value of the TSC counter before and after calling is_core_idle() and calculated the difference. 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 values are expressed in TSC counts, except for 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
The metrics show that both the inline and non-inline versions exhibit similar performance characteristics. --- Changes since v3: * None
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 | 13 ++++++++++--- 2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index 719147460ca8..986344ebf2f6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2461,4 +2461,6 @@ 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 da3e009eef42..a52589a6c561 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; @@ -9652,7 +9659,7 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu) if (!sched_smt_active()) return true; - return sd->flags & SD_SHARE_CPUCAPACITY || is_core_idle(cpu); + return sd->flags & SD_SHARE_CPUCAPACITY || sched_smt_siblings_idle(cpu); } /** -- 2.25.1
| |