Please ignore my question. I saw the data from discussion.

"Run a copy (single thread) Unixbench, with or without a busy poll program in
its SMT sibling,  and Unixbench score can lower 1/3 with SMT busy polling program"

Dongli Zhang

On 7/22/21 8:07 AM, Dongli Zhang wrote:

Hi RongQing,

Would you mind share if there is any performance data to demonstrate how much
performance can be improved?

Thank you very much!

Dongli Zhang

On 7/21/21 8:58 PM, Li RongQing wrote:

quoted

SMT siblings share caches and other hardware, halt polling
will degrade its sibling performance if its sibling is busy

Signed-off-by: Li RongQing <redacted>
---
 include/linux/kvm_host.h |  5 ++++-
 include/linux/sched.h    | 17 +++++++++++++++++
 kernel/sched/fair.c      | 17 -----------------
 3 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ae7735b..15b3ef4 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h

@@ -269,7 +269,10 @@ static inline bool kvm_vcpu_mapped(struct kvm_host_map *map)
 
 static inline bool kvm_vcpu_can_poll(ktime_t cur, ktime_t stop)
 {
-	return single_task_running() && !need_resched() && ktime_before(cur, stop);
+	return single_task_running() &&
+		   !need_resched() &&
+		   ktime_before(cur, stop) &&
+		   is_core_idle(raw_smp_processor_id());
 }
 
 /*

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ec8d07d..c333218 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -34,6 +34,7 @@
 #include <linux/rseq.h>
 #include <linux/seqlock.h>
 #include <linux/kcsan.h>
+#include <linux/topology.h>
 #include <asm/kmap_size.h>
 
 /* task_struct member predeclarations (sorted alphabetically): */

@@ -2191,6 +2192,22 @@ int sched_trace_rq_nr_running(struct rq *rq);
 
 const struct cpumask *sched_trace_rd_span(struct root_domain *rd);
 
+static inline bool is_core_idle(int cpu)
+{
+#ifdef CONFIG_SCHED_SMT
+	int sibling;
+
+	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
+		if (cpu == sibling)
+			continue;
+
+		if (!idle_cpu(cpu))
+			return false;
+	}
+#endif
+	return true;
+}
+
 #ifdef CONFIG_SCHED_CORE
 extern void sched_core_free(struct task_struct *tsk);
 extern void sched_core_fork(struct task_struct *p);

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 44c4520..5b0259c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c

@@ -1477,23 +1477,6 @@ struct numa_stats {
 	int idle_cpu;
 };
 
-static inline bool is_core_idle(int cpu)
-{
-#ifdef CONFIG_SCHED_SMT
-	int sibling;
-
-	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
-		if (cpu == sibling)
-			continue;
-
-		if (!idle_cpu(cpu))
-			return false;
-	}
-#endif
-
-	return true;
-}
-
 struct task_numa_env {
 	struct task_struct *p;