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sched_ule(4): Fix possible significance loss.

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Before this change kern.sched.interact sysctl setting above 32 gave
all interactive threads identical priority of PRI_MIN_INTERACT due to
((PRI_MAX_INTERACT - PRI_MIN_INTERACT + 1) / sched_interact) turning
zero.  Setting the sysctl lower reduced the range of used priority
levels up to half, that is not great either.

Change of the operations order should fix the issue, always using full
range of priorities, while overflow is impossible there since both
score and priority values are small.  While there, make the variables
unsigned as they really are.

MFC after:	1 month
This commit is contained in:
Alexander Motin 2021-10-01 23:47:18 -04:00
parent 93d120dbc0
commit 1c119e173d
1 changed files with 7 additions and 8 deletions
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15
sys/kern/sched_ule.c
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@ -207,7 +207,7 @@ _Static_assert(sizeof(struct thread) + sizeof(struct td_sched) <=
* sched_slice: Runtime of each thread before rescheduling.
* preempt_thresh: Priority threshold for preemption and remote IPIs.
*/
static int __read_mostly sched_interact = SCHED_INTERACT_THRESH;
static u_int __read_mostly sched_interact = SCHED_INTERACT_THRESH;
static int __read_mostly tickincr = 8 << SCHED_TICK_SHIFT;
static int __read_mostly realstathz = 127; /* reset during boot. */
static int __read_mostly sched_slice = 10; /* reset during boot. */
@ -1616,8 +1616,7 @@ sched_interact_score(struct thread *td)
static void
sched_priority(struct thread *td)
{
int score;
int pri;
u_int pri, score;
if (PRI_BASE(td->td_pri_class) != PRI_TIMESHARE)
return;
@ -1637,10 +1636,10 @@ sched_priority(struct thread *td)
score = imax(0, sched_interact_score(td) + td->td_proc->p_nice);
if (score < sched_interact) {
pri = PRI_MIN_INTERACT;
pri += ((PRI_MAX_INTERACT - PRI_MIN_INTERACT + 1) /
sched_interact) * score;
pri += (PRI_MAX_INTERACT - PRI_MIN_INTERACT + 1) * score /
sched_interact;
KASSERT(pri >= PRI_MIN_INTERACT && pri <= PRI_MAX_INTERACT,
("sched_priority: invalid interactive priority %d score %d",
("sched_priority: invalid interactive priority %u score %u",
pri, score));
} else {
pri = SCHED_PRI_MIN;
@ -1649,7 +1648,7 @@ sched_priority(struct thread *td)
SCHED_PRI_RANGE - 1);
pri += SCHED_PRI_NICE(td->td_proc->p_nice);
KASSERT(pri >= PRI_MIN_BATCH && pri <= PRI_MAX_BATCH,
("sched_priority: invalid priority %d: nice %d, "
("sched_priority: invalid priority %u: nice %d, "
"ticks %d ftick %d ltick %d tick pri %d",
pri, td->td_proc->p_nice, td_get_sched(td)->ts_ticks,
td_get_sched(td)->ts_ftick, td_get_sched(td)->ts_ltick,
@ -3174,7 +3173,7 @@ SYSCTL_PROC(_kern_sched, OID_AUTO, quantum,
"Quantum for timeshare threads in microseconds");
SYSCTL_INT(_kern_sched, OID_AUTO, slice, CTLFLAG_RW, &sched_slice, 0,
"Quantum for timeshare threads in stathz ticks");
SYSCTL_INT(_kern_sched, OID_AUTO, interact, CTLFLAG_RW, &sched_interact, 0,
SYSCTL_UINT(_kern_sched, OID_AUTO, interact, CTLFLAG_RW, &sched_interact, 0,
"Interactivity score threshold");
SYSCTL_INT(_kern_sched, OID_AUTO, preempt_thresh, CTLFLAG_RW,
&preempt_thresh, 0,