git: c72188d85a79 - main - racct: Improve handling of the pcpu resource
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Date: Tue, 05 Aug 2025 23:57:58 UTC
The branch main has been updated by markj:
URL: https://cgit.FreeBSD.org/src/commit/?id=c72188d85a793c7610208beafb83af544de6e3b7
commit c72188d85a793c7610208beafb83af544de6e3b7
Author: Cyril Zhang <cyril@freebsdfoundation.org>
AuthorDate: 2025-08-05 23:20:56 +0000
Commit: Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-08-05 23:33:55 +0000
racct: Improve handling of the pcpu resource
The previous scheme would inflate the CPU consumption of short-lived
processes. For containers (e.g., processes, jails), the total pcpu
usage was computed as a sum of the pcpu usage of all constituent
threads, which makes little sense for a decaying average.
Instead, aggregate wallclock time of all on-CPU threads and compute the
pcpu resource as a decaying average as the sum. This gives much more
reasonable and accurate values in various simple tests.
PR: 235556
Reviewed by: markj
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D30878
---
sys/kern/kern_racct.c | 307 +++++++++++++++++++++++++-------------------------
sys/sys/proc.h | 1 -
sys/sys/racct.h | 6 +-
3 files changed, 156 insertions(+), 158 deletions(-)
diff --git a/sys/kern/kern_racct.c b/sys/kern/kern_racct.c
index 7ee3b9e2048a..7351e9cb6313 100644
--- a/sys/kern/kern_racct.c
+++ b/sys/kern/kern_racct.c
@@ -96,6 +96,13 @@ static void racct_sub_cred_locked(struct ucred *cred, int resource,
uint64_t amount);
static void racct_add_cred_locked(struct ucred *cred, int resource,
uint64_t amount);
+static int racct_set_locked(struct proc *p, int resource, uint64_t amount,
+ int force);
+static void racct_updatepcpu_locked(struct proc *p);
+static void racct_updatepcpu_racct_locked(struct racct *racct);
+static void racct_updatepcpu_containers(void);
+static void racct_settime_locked(struct proc *p, bool exit);
+static void racct_zeropcpu_locked(struct proc *p);
SDT_PROVIDER_DEFINE(racct);
SDT_PROBE_DEFINE3(racct, , rusage, add,
@@ -308,68 +315,6 @@ fixpt_t ccpu_exp[] = {
#define CCPU_EXP_MAX 110
-/*
- * This function is analogical to the getpcpu() function in the ps(1) command.
- * They should both calculate in the same way so that the racct %cpu
- * calculations are consistent with the values shown by the ps(1) tool.
- * The calculations are more complex in the 4BSD scheduler because of the value
- * of the ccpu variable. In ULE it is defined to be zero which saves us some
- * work.
- */
-static uint64_t
-racct_getpcpu(struct proc *p, u_int pcpu)
-{
- u_int swtime;
-#ifdef SCHED_4BSD
- fixpt_t pctcpu, pctcpu_next;
-#endif
- fixpt_t p_pctcpu;
- struct thread *td;
-
- ASSERT_RACCT_ENABLED();
- KASSERT((p->p_flag & P_IDLEPROC) == 0,
- ("racct_getpcpu: idle process %p", p));
-
- swtime = (ticks - p->p_swtick) / hz;
-
- /*
- * For short-lived processes, the sched_pctcpu() returns small
- * values even for cpu intensive processes. Therefore we use
- * our own estimate in this case.
- */
- if (swtime < RACCT_PCPU_SECS)
- return (pcpu);
-
- p_pctcpu = 0;
- FOREACH_THREAD_IN_PROC(p, td) {
- thread_lock(td);
-#ifdef SCHED_4BSD
- pctcpu = sched_pctcpu(td);
- /* Count also the yet unfinished second. */
- pctcpu_next = (pctcpu * ccpu_exp[1]) >> FSHIFT;
- pctcpu_next += sched_pctcpu_delta(td);
- p_pctcpu += max(pctcpu, pctcpu_next);
-#else
- /*
- * In ULE the %cpu statistics are updated on every
- * sched_pctcpu() call. So special calculations to
- * account for the latest (unfinished) second are
- * not needed.
- */
- p_pctcpu += sched_pctcpu(td);
-#endif
- thread_unlock(td);
- }
-
-#ifdef SCHED_4BSD
- if (swtime <= CCPU_EXP_MAX)
- return ((100 * (uint64_t)p_pctcpu * 1000000) /
- (FSCALE - ccpu_exp[swtime]));
-#endif
-
- return ((100 * (uint64_t)p_pctcpu * 1000000) / FSCALE);
-}
-
static void
racct_add_racct(struct racct *dest, const struct racct *src)
{
@@ -499,19 +444,6 @@ racct_adjust_resource(struct racct *racct, int resource,
("%s: resource %d usage < 0", __func__, resource));
racct->r_resources[resource] = 0;
}
-
- /*
- * There are some cases where the racct %cpu resource would grow
- * beyond 100% per core. For example in racct_proc_exit() we add
- * the process %cpu usage to the ucred racct containers. If too
- * many processes terminated in a short time span, the ucred %cpu
- * resource could grow too much. Also, the 4BSD scheduler sometimes
- * returns for a thread more than 100% cpu usage. So we set a sane
- * boundary here to 100% * the maximum number of CPUs.
- */
- if ((resource == RACCT_PCTCPU) &&
- (racct->r_resources[RACCT_PCTCPU] > 100 * 1000000 * (int64_t)MAXCPU))
- racct->r_resources[RACCT_PCTCPU] = 100 * 1000000 * (int64_t)MAXCPU;
}
static int
@@ -635,10 +567,44 @@ racct_add_buf(struct proc *p, const struct buf *bp, int is_write)
RACCT_UNLOCK();
}
+static void
+racct_settime_locked(struct proc *p, bool exit)
+{
+ struct thread *td;
+ struct timeval wallclock;
+ uint64_t runtime;
+
+ ASSERT_RACCT_ENABLED();
+ RACCT_LOCK_ASSERT();
+ PROC_LOCK_ASSERT(p, MA_OWNED);
+
+ if (exit) {
+ /*
+ * proc_reap() has already calculated rux
+ * and added crux to rux.
+ */
+ runtime = cputick2usec(p->p_rux.rux_runtime -
+ p->p_crux.rux_runtime);
+ } else {
+ PROC_STATLOCK(p);
+ FOREACH_THREAD_IN_PROC(p, td)
+ ruxagg(p, td);
+ PROC_STATUNLOCK(p);
+ runtime = cputick2usec(p->p_rux.rux_runtime);
+ }
+ microuptime(&wallclock);
+ timevalsub(&wallclock, &p->p_stats->p_start);
+
+ racct_set_locked(p, RACCT_CPU, runtime, 0);
+ racct_set_locked(p, RACCT_WALLCLOCK,
+ (uint64_t)wallclock.tv_sec * 1000000 +
+ wallclock.tv_usec, 0);
+}
+
static int
racct_set_locked(struct proc *p, int resource, uint64_t amount, int force)
{
- int64_t old_amount, decayed_amount, diff_proc, diff_cred;
+ int64_t old_amount, diff_proc, diff_cred;
#ifdef RCTL
int error;
#endif
@@ -655,17 +621,7 @@ racct_set_locked(struct proc *p, int resource, uint64_t amount, int force)
* The diffs may be negative.
*/
diff_proc = amount - old_amount;
- if (resource == RACCT_PCTCPU) {
- /*
- * Resources in per-credential racct containers may decay.
- * If this is the case, we need to calculate the difference
- * between the new amount and the proportional value of the
- * old amount that has decayed in the ucred racct containers.
- */
- decayed_amount = old_amount * RACCT_DECAY_FACTOR / FSCALE;
- diff_cred = amount - decayed_amount;
- } else
- diff_cred = diff_proc;
+ diff_cred = diff_proc;
#ifdef notyet
KASSERT(diff_proc >= 0 || RACCT_CAN_DROP(resource),
("%s: usage of non-droppable resource %d dropping", __func__,
@@ -908,8 +864,6 @@ racct_proc_fork(struct proc *parent, struct proc *child)
goto out;
#endif
- /* Init process cpu time. */
- child->p_prev_runtime = 0;
child->p_throttled = 0;
/*
@@ -964,37 +918,16 @@ racct_proc_fork_done(struct proc *child)
void
racct_proc_exit(struct proc *p)
{
- struct timeval wallclock;
- uint64_t pct_estimate, pct, runtime;
int i;
if (!racct_enable)
return;
PROC_LOCK(p);
- /*
- * We don't need to calculate rux, proc_reap() has already done this.
- */
- runtime = cputick2usec(p->p_rux.rux_runtime);
-#ifdef notyet
- KASSERT(runtime >= p->p_prev_runtime, ("runtime < p_prev_runtime"));
-#else
- if (runtime < p->p_prev_runtime)
- runtime = p->p_prev_runtime;
-#endif
- microuptime(&wallclock);
- timevalsub(&wallclock, &p->p_stats->p_start);
- if (wallclock.tv_sec > 0 || wallclock.tv_usec > 0) {
- pct_estimate = (1000000 * runtime * 100) /
- ((uint64_t)wallclock.tv_sec * 1000000 +
- wallclock.tv_usec);
- } else
- pct_estimate = 0;
- pct = racct_getpcpu(p, pct_estimate);
-
RACCT_LOCK();
- racct_set_locked(p, RACCT_CPU, runtime, 0);
- racct_add_cred_locked(p->p_ucred, RACCT_PCTCPU, pct);
+
+ racct_settime_locked(p, true);
+ racct_zeropcpu_locked(p);
KASSERT(p->p_racct->r_resources[RACCT_RSS] == 0,
("process reaped with %ju allocated for RSS\n",
@@ -1068,6 +1001,10 @@ racct_move(struct racct *dest, struct racct *src)
RACCT_LOCK();
racct_add_racct(dest, src);
racct_sub_racct(src, src);
+ dest->r_runtime = src->r_runtime;
+ dest->r_time = src->r_time;
+ src->r_runtime = 0;
+ timevalsub(&src->r_time, &src->r_time);
RACCT_UNLOCK();
}
@@ -1170,8 +1107,6 @@ racct_proc_wakeup(struct proc *p)
static void
racct_decay_callback(struct racct *racct, void *dummy1, void *dummy2)
{
- int64_t r_old, r_new;
-
ASSERT_RACCT_ENABLED();
RACCT_LOCK_ASSERT();
@@ -1181,15 +1116,6 @@ racct_decay_callback(struct racct *racct, void *dummy1, void *dummy2)
rctl_throttle_decay(racct, RACCT_READIOPS);
rctl_throttle_decay(racct, RACCT_WRITEIOPS);
#endif
-
- r_old = racct->r_resources[RACCT_PCTCPU];
-
- /* If there is nothing to decay, just exit. */
- if (r_old <= 0)
- return;
-
- r_new = r_old * RACCT_DECAY_FACTOR / FSCALE;
- racct->r_resources[RACCT_PCTCPU] = r_new;
}
static void
@@ -1220,16 +1146,106 @@ racct_decay(void)
racct_decay_post, NULL, NULL);
}
+static void
+racct_updatepcpu_racct_locked(struct racct *racct)
+{
+ struct timeval diff;
+ uint64_t elapsed;
+ uint64_t runtime;
+ uint64_t newpcpu;
+ uint64_t oldpcpu;
+
+ ASSERT_RACCT_ENABLED();
+ RACCT_LOCK_ASSERT();
+
+ /* Difference between now and previously-recorded time. */
+ microuptime(&diff);
+ timevalsub(&diff, &racct->r_time);
+ elapsed = (uint64_t)diff.tv_sec * 1000000 + diff.tv_usec;
+
+ /* Difference between current and previously-recorded runtime. */
+ runtime = racct->r_resources[RACCT_CPU] - racct->r_runtime;
+
+ newpcpu = runtime * 100 * 1000000 / elapsed;
+ oldpcpu = racct->r_resources[RACCT_PCTCPU];
+ /*
+ * This calculation is equivalent to
+ * (1 - 0.3) * newpcpu + 0.3 * oldpcpu
+ * where RACCT_DECAY_FACTOR = 0.3 * FSCALE.
+ */
+ racct->r_resources[RACCT_PCTCPU] = ((FSCALE - RACCT_DECAY_FACTOR) *
+ newpcpu + RACCT_DECAY_FACTOR * oldpcpu) / FSCALE;
+ if (racct->r_resources[RACCT_PCTCPU] >
+ 100 * 1000000 * (uint64_t)mp_ncpus)
+ racct->r_resources[RACCT_PCTCPU] = 100 * 1000000 *
+ (uint64_t)mp_ncpus;
+
+ /* Record current times. */
+ racct->r_runtime = racct->r_resources[RACCT_CPU];
+ timevaladd(&racct->r_time, &diff);
+}
+
+static void
+racct_zeropcpu_locked(struct proc *p)
+{
+ ASSERT_RACCT_ENABLED();
+ PROC_LOCK_ASSERT(p, MA_OWNED);
+
+ p->p_racct->r_resources[RACCT_PCTCPU] = 0;
+}
+
+static void
+racct_updatepcpu_locked(struct proc *p)
+{
+ ASSERT_RACCT_ENABLED();
+ PROC_LOCK_ASSERT(p, MA_OWNED);
+
+ racct_updatepcpu_racct_locked(p->p_racct);
+}
+
+static void
+racct_updatepcpu_pre(void)
+{
+
+ RACCT_LOCK();
+}
+
+static void
+racct_updatepcpu_post(void)
+{
+
+ RACCT_UNLOCK();
+}
+
+static void
+racct_updatepcpu_racct_callback(struct racct *racct, void *dummy1, void *dummy2)
+{
+ racct_updatepcpu_racct_locked(racct);
+}
+
+static void
+racct_updatepcpu_containers(void)
+{
+ ASSERT_RACCT_ENABLED();
+
+ ui_racct_foreach(racct_updatepcpu_racct_callback, racct_updatepcpu_pre,
+ racct_updatepcpu_post, NULL, NULL);
+ loginclass_racct_foreach(racct_updatepcpu_racct_callback, racct_updatepcpu_pre,
+ racct_updatepcpu_post, NULL, NULL);
+ prison_racct_foreach(racct_updatepcpu_racct_callback, racct_updatepcpu_pre,
+ racct_updatepcpu_post, NULL, NULL);
+}
+
static void
racctd(void)
{
- struct thread *td;
struct proc *p;
- struct timeval wallclock;
- uint64_t pct, pct_estimate, runtime;
+ struct proc *idle;
ASSERT_RACCT_ENABLED();
+ idle = STAILQ_FIRST(&cpuhead)->pc_idlethread->td_proc;
+
for (;;) {
racct_decay();
@@ -1237,36 +1253,16 @@ racctd(void)
FOREACH_PROC_IN_SYSTEM(p) {
PROC_LOCK(p);
+ if (p == idle) {
+ PROC_UNLOCK(p);
+ continue;
+ }
if (p->p_state != PRS_NORMAL ||
(p->p_flag & P_IDLEPROC) != 0) {
- if (p->p_state == PRS_ZOMBIE)
- racct_set(p, RACCT_PCTCPU, 0);
PROC_UNLOCK(p);
continue;
}
- microuptime(&wallclock);
- timevalsub(&wallclock, &p->p_stats->p_start);
- PROC_STATLOCK(p);
- FOREACH_THREAD_IN_PROC(p, td)
- ruxagg(p, td);
- runtime = cputick2usec(p->p_rux.rux_runtime);
- PROC_STATUNLOCK(p);
-#ifdef notyet
- KASSERT(runtime >= p->p_prev_runtime,
- ("runtime < p_prev_runtime"));
-#else
- if (runtime < p->p_prev_runtime)
- runtime = p->p_prev_runtime;
-#endif
- p->p_prev_runtime = runtime;
- if (wallclock.tv_sec > 0 || wallclock.tv_usec > 0) {
- pct_estimate = (1000000 * runtime * 100) /
- ((uint64_t)wallclock.tv_sec * 1000000 +
- wallclock.tv_usec);
- } else
- pct_estimate = 0;
- pct = racct_getpcpu(p, pct_estimate);
RACCT_LOCK();
#ifdef RCTL
rctl_throttle_decay(p->p_racct, RACCT_READBPS);
@@ -1274,11 +1270,8 @@ racctd(void)
rctl_throttle_decay(p->p_racct, RACCT_READIOPS);
rctl_throttle_decay(p->p_racct, RACCT_WRITEIOPS);
#endif
- racct_set_locked(p, RACCT_PCTCPU, pct, 1);
- racct_set_locked(p, RACCT_CPU, runtime, 0);
- racct_set_locked(p, RACCT_WALLCLOCK,
- (uint64_t)wallclock.tv_sec * 1000000 +
- wallclock.tv_usec, 0);
+ racct_settime_locked(p, false);
+ racct_updatepcpu_locked(p);
RACCT_UNLOCK();
PROC_UNLOCK(p);
}
@@ -1306,6 +1299,8 @@ racctd(void)
PROC_UNLOCK(p);
}
sx_sunlock(&allproc_lock);
+
+ racct_updatepcpu_containers();
pause("-", hz);
}
}
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index af9cafa99dd0..9140cee56885 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -763,7 +763,6 @@ struct proc {
LIST_HEAD(, mqueue_notifier) p_mqnotifier; /* (c) mqueue notifiers.*/
struct kdtrace_proc *p_dtrace; /* (*) DTrace-specific data. */
struct cv p_pwait; /* (*) wait cv for exit/exec. */
- uint64_t p_prev_runtime; /* (c) Resource usage accounting. */
struct racct *p_racct; /* (b) Resource accounting. */
int p_throttled; /* (c) Flag for racct pcpu throttling */
/*
diff --git a/sys/sys/racct.h b/sys/sys/racct.h
index c6020b82c865..92b50353774e 100644
--- a/sys/sys/racct.h
+++ b/sys/sys/racct.h
@@ -141,13 +141,17 @@ extern bool racct_enable;
/*
* The 'racct' structure defines resource consumption for a particular
- * subject, such as process or jail.
+ * subject, such as process or jail. It also contains the total
+ * cpu time and real time of the subject, recorded at the most recent
+ * time that RACCT_PCPU was updated.
*
* This structure must be filled with zeroes initially.
*/
struct racct {
int64_t r_resources[RACCT_MAX + 1];
LIST_HEAD(, rctl_rule_link) r_rule_links;
+ uint64_t r_runtime;
+ struct timeval r_time;
};
SYSCTL_DECL(_kern_racct);