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Index: sys/kern/sched_4bsd.c
===================================================================
--- sys/kern/sched_4bsd.c
+++ sys/kern/sched_4bsd.c
@@ -42,6 +42,7 @@
#include <sys/param.h>
#include <sys/systm.h>
+#include <sys/counter.h>
#include <sys/cpuset.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
@@ -262,6 +263,19 @@
"allow threads to share a quantum");
#endif
+SYSCTL_NODE(_kern_sched, OID_AUTO, ithread, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
+ "Interrupt thread stats");
+
+static COUNTER_U64_DEFINE_EARLY(ithread_demotions);
+SYSCTL_COUNTER_U64(_kern_sched_ithread, OID_AUTO, demotions,
+ CTLFLAG_RD, &ithread_demotions,
+ "Count of interrupt thread priority demotions");
+
+static COUNTER_U64_DEFINE_EARLY(ithread_preemptions);
+SYSCTL_COUNTER_U64(_kern_sched_ithread, OID_AUTO, preemptions,
+ CTLFLAG_RD, &ithread_preemptions,
+ "Count of interrupt thread preemptions due to time-sharing");
+
SDT_PROVIDER_DEFINE(sched);
SDT_PROBE_DEFINE3(sched, , , change__pri, "struct thread *",
@@ -739,7 +753,20 @@
*/
if (!TD_IS_IDLETHREAD(td) && --ts->ts_slice <= 0) {
ts->ts_slice = sched_slice;
- td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
+
+ /*
+ * If an ithread uses a full quantum, demote its
+ * priority and preempt it.
+ */
+ if (PRI_BASE(td->td_pri_class) == PRI_ITHD) {
+ counter_u64_add(ithread_preemptions, 1);
+ td->td_owepreempt = 1;
+ if (td->td_base_pri + RQ_PPQ < PRI_MAX_ITHD) {
+ counter_u64_add(ithread_demotions, 1);
+ sched_prio(td, td->td_base_pri + RQ_PPQ);
+ }
+ } else
+ td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
}
stat = DPCPU_PTR(idlestat);
@@ -1134,6 +1161,15 @@
td->td_slptick = 0;
ts->ts_slptime = 0;
ts->ts_slice = sched_slice;
+
+ /*
+ * When resuming an idle ithread, restore its base ithread
+ * priority.
+ */
+ if (PRI_BASE(td->td_pri_class) == PRI_ITHD &&
+ td->td_base_pri != td->td_base_ithread_pri)
+ sched_prio(td, td->td_base_ithread_pri);
+
sched_add(td, srqflags);
}

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