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Improve timeout precision of pthread_cond_timedwait().

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This code was not touched when all other user-space sleep functions were
switched to sbintime_t and decoupled from hardclock.  When it is possible,
convert supplied times into sbinuptime to supply directly to msleep_sbt()
with C_ABSOLUTE.  This provides the timeout resolution of few microseconds
instead of 2 milliseconds, plus avoids few clock reads and conversions.

Reviewed by:	vangyzen
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D34163
This commit is contained in:
Alexander Motin 2022-03-03 22:03:09 -05:00
parent 0b25cbc79d
commit 56070dd2e4
1 changed files with 82 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

130
sys/kern/kern_umtx.c
View File

@ -175,8 +175,6 @@ static SYSCTL_NODE(_debug_umtx, OID_AUTO, chains, CTLFLAG_RD | CTLFLAG_MPSAFE, 0
static inline void umtx_abs_timeout_init2(struct umtx_abs_timeout *timo,
const struct _umtx_time *umtxtime);
static int umtx_abs_timeout_gethz(struct umtx_abs_timeout *timo);
static inline void umtx_abs_timeout_update(struct umtx_abs_timeout *timo);
static void umtx_shm_init(void);
static void umtxq_sysinit(void *);
@ -683,20 +681,14 @@ umtx_abs_timeout_init(struct umtx_abs_timeout *timo, int clockid,
timo->clockid = clockid;
if (!absolute) {
timo->is_abs_real = false;
umtx_abs_timeout_update(timo);
kern_clock_gettime(curthread, timo->clockid, &timo->cur);
timespecadd(&timo->cur, timeout, &timo->end);
} else {
timo->end = *timeout;
timo->is_abs_real = clockid == CLOCK_REALTIME ||
clockid == CLOCK_REALTIME_FAST ||
clockid == CLOCK_REALTIME_PRECISE;
/*
* If is_abs_real, umtxq_sleep will read the clock
* after setting td_rtcgen; otherwise, read it here.
*/
if (!timo->is_abs_real) {
umtx_abs_timeout_update(timo);
}
clockid == CLOCK_REALTIME_PRECISE ||
clockid == CLOCK_SECOND;
}
}
@ -709,22 +701,71 @@ umtx_abs_timeout_init2(struct umtx_abs_timeout *timo,
(umtxtime->_flags & UMTX_ABSTIME) != 0, &umtxtime->_timeout);
}
static void
umtx_abs_timeout_update(struct umtx_abs_timeout *timo)
{
kern_clock_gettime(curthread, timo->clockid, &timo->cur);
}
static int
umtx_abs_timeout_gethz(struct umtx_abs_timeout *timo)
umtx_abs_timeout_getsbt(struct umtx_abs_timeout *timo, sbintime_t *sbt,
int *flags)
{
struct bintime bt, bbt;
struct timespec tts;
if (timespeccmp(&timo->end, &timo->cur, <=))
return (-1);
timespecsub(&timo->end, &timo->cur, &tts);
return (tstohz(&tts));
switch (timo->clockid) {
/* Clocks that can be converted into absolute time. */
case CLOCK_REALTIME:
case CLOCK_REALTIME_PRECISE:
case CLOCK_REALTIME_FAST:
case CLOCK_MONOTONIC:
case CLOCK_MONOTONIC_PRECISE:
case CLOCK_MONOTONIC_FAST:
case CLOCK_UPTIME:
case CLOCK_UPTIME_PRECISE:
case CLOCK_UPTIME_FAST:
case CLOCK_SECOND:
timespec2bintime(&timo->end, &bt);
switch (timo->clockid) {
case CLOCK_REALTIME:
case CLOCK_REALTIME_PRECISE:
case CLOCK_REALTIME_FAST:
case CLOCK_SECOND:
getboottimebin(&bbt);
bintime_sub(&bt, &bbt);
break;
}
if (bt.sec < 0)
return (ETIMEDOUT);
if (bt.sec >= (SBT_MAX >> 32)) {
*sbt = 0;
*flags = 0;
return (0);
}
*sbt = bttosbt(bt);
switch (timo->clockid) {
case CLOCK_REALTIME_FAST:
case CLOCK_MONOTONIC_FAST:
case CLOCK_UPTIME_FAST:
*sbt += tc_tick_sbt;
break;
case CLOCK_SECOND:
*sbt += SBT_1S;
break;
}
*flags = C_ABSOLUTE;
return (0);
/* Clocks that has to be periodically polled. */
case CLOCK_VIRTUAL:
case CLOCK_PROF:
case CLOCK_THREAD_CPUTIME_ID:
case CLOCK_PROCESS_CPUTIME_ID:
default:
kern_clock_gettime(curthread, timo->clockid, &timo->cur);
if (timespeccmp(&timo->end, &timo->cur, <=))
return (ETIMEDOUT);
timespecsub(&timo->end, &timo->cur, &tts);
*sbt = tick_sbt * tstohz(&tts);
*flags = C_HARDCLOCK;
return (0);
}
}
static uint32_t
@ -746,15 +787,11 @@ umtx_unlock_val(uint32_t flags, bool rb)
*/
int
umtxq_sleep(struct umtx_q *uq, const char *wmesg,
struct umtx_abs_timeout *abstime)
struct umtx_abs_timeout *timo)
{
struct umtxq_chain *uc;
int error, timo;
if (abstime != NULL && abstime->is_abs_real) {
curthread->td_rtcgen = atomic_load_acq_int(&rtc_generation);
umtx_abs_timeout_update(abstime);
}
sbintime_t sbt = 0;
int error, flags = 0;
uc = umtxq_getchain(&uq->uq_key);
UMTXQ_LOCKED_ASSERT(uc);
@ -763,26 +800,22 @@ umtxq_sleep(struct umtx_q *uq, const char *wmesg,
error = 0;
break;
}
if (abstime != NULL) {
timo = umtx_abs_timeout_gethz(abstime);
if (timo < 0) {
error = ETIMEDOUT;
break;
}
} else
timo = 0;
error = msleep(uq, &uc->uc_lock, PCATCH | PDROP, wmesg, timo);
if (error == EINTR || error == ERESTART) {
umtxq_lock(&uq->uq_key);
break;
}
if (abstime != NULL) {
if (abstime->is_abs_real)
if (timo != NULL) {
if (timo->is_abs_real)
curthread->td_rtcgen =
atomic_load_acq_int(&rtc_generation);
umtx_abs_timeout_update(abstime);
error = umtx_abs_timeout_getsbt(timo, &sbt, &flags);
if (error != 0)
break;
}
error = msleep_sbt(uq, &uc->uc_lock, PCATCH, wmesg,
sbt, 0, flags);
if (error == EINTR || error == ERESTART)
break;
if (error == EWOULDBLOCK && (flags & C_ABSOLUTE) != 0) {
error = ETIMEDOUT;
break;
}
umtxq_lock(&uq->uq_key);
}
curthread->td_rtcgen = 0;
@ -3652,7 +3685,8 @@ do_sem2_wait(struct thread *td, struct _usem2 *sem, struct _umtx_time *timeout)
if (error == ERESTART)
error = EINTR;
if (error == EINTR) {
umtx_abs_timeout_update(&timo);
kern_clock_gettime(curthread, timo.clockid,
&timo.cur);
timespecsub(&timo.end, &timo.cur,
&timeout->_timeout);
}