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ule: Simplistic time-sharing for interrupt threads.

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If an interrupt thread runs for a full quantum without yielding the
CPU, demote its priority and schedule a preemption to give other
ithreads a turn.

Reviewed by:	kib, markj
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D35644
This commit is contained in:
John Baldwin 2022-07-14 13:13:57 -07:00
parent ed998d1c24
commit 954cffe95d
1 changed files with 41 additions and 3 deletions
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44
sys/kern/sched_ule.c
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@ -2375,6 +2375,15 @@ sched_wakeup(struct thread *td, int srqflags)
sched_interact_update(td);
sched_pctcpu_update(ts, 0);
}
/*
* When resuming an idle ithread, restore its base ithread
* priority.
*/
if (PRI_BASE(td->td_pri_class) == PRI_ITHD &&
td->td_priority != td->td_base_ithread_pri)
sched_prio(td, td->td_base_ithread_pri);
/*
* Reset the slice value since we slept and advanced the round-robin.
*/
@ -2542,9 +2551,25 @@ sched_userret_slowpath(struct thread *td)
thread_unlock(td);
}
SCHED_STAT_DEFINE(ithread_demotions, "Interrupt thread priority demotions");
SCHED_STAT_DEFINE(ithread_preemptions,
"Interrupt thread preemptions due to time-sharing");
/*
* Return time slice for a given thread. For ithreads this is
* sched_slice. For other threads it is tdq_slice(tdq).
*/
static inline int
td_slice(struct thread *td, struct tdq *tdq)
{
if (PRI_BASE(td->td_pri_class) == PRI_ITHD)
return (sched_slice);
return (tdq_slice(tdq));
}
/*
* Handle a stathz tick. This is really only relevant for timeshare
* threads.
* and interrupt threads.
*/
void
sched_clock(struct thread *td, int cnt)
@ -2602,9 +2627,22 @@ sched_clock(struct thread *td, int cnt)
* time slice (default is 100ms).
*/
ts->ts_slice += cnt;
if (ts->ts_slice >= tdq_slice(tdq)) {
if (ts->ts_slice >= td_slice(td, tdq)) {
ts->ts_slice = 0;
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) {
SCHED_STAT_INC(ithread_preemptions);
td->td_owepreempt = 1;
if (td->td_base_pri + RQ_PPQ < PRI_MAX_ITHD) {
SCHED_STAT_INC(ithread_demotions);
sched_prio(td, td->td_base_pri + RQ_PPQ);
}
} else
td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
}
}