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4bsd: 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
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D35645
This commit is contained in:
John Baldwin 2022-07-14 13:14:17 -07:00
parent 954cffe95d
commit 40efe74352
1 changed files with 27 additions and 1 deletions
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28
sys/kern/sched_4bsd.c
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@ -703,6 +703,10 @@ sched_rr_interval(void)
return (imax(1, (sched_slice * hz + realstathz / 2) / realstathz));
}
SCHED_STAT_DEFINE(ithread_demotions, "Interrupt thread priority demotions");
SCHED_STAT_DEFINE(ithread_preemptions,
"Interrupt thread preemptions due to time-sharing");
/*
* We adjust the priority of the current process. The priority of a
* process gets worse as it accumulates CPU time. The cpu usage
@ -739,7 +743,20 @@ sched_clock_tick(struct thread *td)
*/
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) {
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;
}
stat = DPCPU_PTR(idlestat);
@ -1134,6 +1151,15 @@ sched_wakeup(struct thread *td, int srqflags)
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);
}