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- Change ULE to use dynamic slice sizes for the timeshare queue in order

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to further reduce latency for threads in this queue.  This should help
   as threads transition from realtime to timeshare.  The latency is
   bound to a max of sched_slice until we have more than sched_slice / 6
   threads runnable.  Then the min slice is allotted to all threads and
   latency becomes (nthreads - 1) * min_slice.

Discussed with: mav
This commit is contained in:
Jeff Roberson 2012-11-08 01:46:47 +00:00
parent 40b43503c0
commit 5e5c387373
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=242736
1 changed files with 48 additions and 10 deletions
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58
sys/kern/sched_ule.c
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@ -189,6 +189,12 @@ static struct td_sched td_sched0;
#define SCHED_INTERACT_HALF (SCHED_INTERACT_MAX / 2)
#define SCHED_INTERACT_THRESH (30)
/*
* These parameters determine the slice behavior for batch work.
*/
#define SCHED_SLICE_DEFAULT_DIVISOR 10 /* ~94 ms, 12 stathz ticks. */
#define SCHED_SLICE_MIN_DIVISOR 6 /* DEFAULT/MIN = ~16 ms. */
/* Flags kept in td_flags. */
#define TDF_SLICEEND TDF_SCHED2 /* Thread time slice is over. */
@ -201,9 +207,10 @@ static struct td_sched td_sched0;
* preempt_thresh: Priority threshold for preemption and remote IPIs.
*/
static int sched_interact = SCHED_INTERACT_THRESH;
static int realstathz = 127;
static int tickincr = 8 << SCHED_TICK_SHIFT;
static int sched_slice = 12;
static int realstathz = 127; /* reset during boot. */
static int sched_slice = 10; /* reset during boot. */
static int sched_slice_min = 1; /* reset during boot. */
#ifdef PREEMPTION
#ifdef FULL_PREEMPTION
static int preempt_thresh = PRI_MAX_IDLE;
@ -558,6 +565,30 @@ tdq_load_rem(struct tdq *tdq, struct thread *td)
SDT_PROBE2(sched, , , load_change, (int)TDQ_ID(tdq), tdq->tdq_load);
}
/*
* Bound timeshare latency by decreasing slice size as load increases. We
* consider the maximum latency as the sum of the threads waiting to run
* aside from curthread and target no more than sched_slice latency but
* no less than sched_slice_min runtime.
*/
static inline int
tdq_slice(struct tdq *tdq)
{
int load;
/*
* It is safe to use sys_load here because this is called from
* contexts where timeshare threads are running and so there
* cannot be higher priority load in the system.
*/
load = tdq->tdq_sysload - 1;
if (load >= SCHED_SLICE_MIN_DIVISOR)
return (sched_slice_min);
if (load <= 1)
return (sched_slice);
return (sched_slice / load);
}
/*
* Set lowpri to its exact value by searching the run-queue and
* evaluating curthread. curthread may be passed as an optimization.
@ -1384,7 +1415,8 @@ sched_initticks(void *dummy)
int incr;
realstathz = stathz ? stathz : hz;
sched_slice = realstathz / 10; /* ~100ms */
sched_slice = realstathz / SCHED_SLICE_DEFAULT_DIVISOR;
sched_slice_min = sched_slice / SCHED_SLICE_MIN_DIVISOR;
hogticks = imax(1, (2 * hz * sched_slice + realstathz / 2) /
realstathz);
@ -1585,7 +1617,7 @@ schedinit(void)
thread0.td_sched = &td_sched0;
td_sched0.ts_ltick = ticks;
td_sched0.ts_ftick = ticks;
td_sched0.ts_slice = sched_slice;
td_sched0.ts_slice = 0;
}
/*
@ -2003,8 +2035,10 @@ sched_wakeup(struct thread *td)
sched_interact_update(td);
sched_pctcpu_update(ts, 0);
}
/* Reset the slice value after we sleep. */
ts->ts_slice = sched_slice;
/*
* Reset the slice value since we slept and advanced the round-robin.
*/
ts->ts_slice = 0;
sched_add(td, SRQ_BORING);
}
@ -2036,14 +2070,16 @@ sched_fork_thread(struct thread *td, struct thread *child)
{
struct td_sched *ts;
struct td_sched *ts2;
struct tdq *tdq;
tdq = TDQ_SELF();
THREAD_LOCK_ASSERT(td, MA_OWNED);
/*
* Initialize child.
*/
ts = td->td_sched;
ts2 = child->td_sched;
child->td_lock = TDQ_LOCKPTR(TDQ_SELF());
child->td_lock = TDQ_LOCKPTR(tdq);
child->td_cpuset = cpuset_ref(td->td_cpuset);
ts2->ts_cpu = ts->ts_cpu;
ts2->ts_flags = 0;
@ -2062,7 +2098,8 @@ sched_fork_thread(struct thread *td, struct thread *child)
*/
ts2->ts_slptime = ts->ts_slptime;
ts2->ts_runtime = ts->ts_runtime;
ts2->ts_slice = 1; /* Attempt to quickly learn interactivity. */
/* Attempt to quickly learn interactivity. */
ts2->ts_slice = tdq_slice(tdq) - sched_slice_min;
#ifdef KTR
bzero(ts2->ts_name, sizeof(ts2->ts_name));
#endif
@ -2227,8 +2264,8 @@ sched_clock(struct thread *td)
* Force a context switch if the current thread has used up a full
* time slice (default is 100ms).
*/
if (!TD_IS_IDLETHREAD(td) && --ts->ts_slice <= 0) {
ts->ts_slice = sched_slice;
if (!TD_IS_IDLETHREAD(td) && ++ts->ts_slice >= tdq_slice(tdq)) {
ts->ts_slice = 0;
td->td_flags |= TDF_NEEDRESCHED | TDF_SLICEEND;
}
}
@ -2799,6 +2836,7 @@ sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
if (new_val <= 0)
return (EINVAL);
sched_slice = imax(1, (new_val + period / 2) / period);
sched_slice_min = sched_slice / SCHED_SLICE_MIN_DIVISOR;
hogticks = imax(1, (2 * hz * sched_slice + realstathz / 2) /
realstathz);
return (0);