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dt: Use one ringbuffer per CPU
Hi,
here is an updated version. It incorporates the diff to continue reading
events from where we left off in a previous read(2) (from [1]).
[1] https://marc.info/?l=openbsd-tech&m=172642998727042
- Christian
---
sys/dev/dt/dt_dev.c | 164 +++++++++++++++++++++++++++++++---------------------
sys/dev/dt/dtvar.h | 9 ---
2 files changed, 98 insertions(+), 75 deletions(-)
diff --git a/sys/dev/dt/dt_dev.c b/sys/dev/dt/dt_dev.c
index 05ce734abf44..c0357239b98e 100644
--- a/sys/dev/dt/dt_dev.c
+++ b/sys/dev/dt/dt_dev.c
@@ -85,14 +85,34 @@
#define DPRINTF(x...) /* nothing */
+/*
+ * Event states ring
+ *
+ * Locks used to protect struct members:
+ * a atomic
+ * r owned by read(2) proc
+ * c owned by CPU
+ * s sliced ownership, based on read/write indexes
+ */
+struct dt_ringbuf {
+ unsigned int dr_prod; /* [a,r] read index */
+ unsigned int dr_cons; /* [a,c] write index */
+ struct dt_evt *dr_ring; /* [s] ring of event states */
+ int dr_block; /* [c] block nested events */
+
+ /* Counters */
+ unsigned int dr_dropevt; /* [a] # of dropped events */
+};
+
/*
* Descriptor associated with each program opening /dev/dt. It is used
* to keep track of enabled PCBs.
*
* Locks used to protect struct members in this file:
* a atomic
- * m per-softc mutex
* K kernel lock
+ * r owned by read(2) proc
+ * I invariant after initialization
*/
struct dt_softc {
SLIST_ENTRY(dt_softc) ds_next; /* [K] descriptor list */
@@ -100,15 +120,16 @@ struct dt_softc {
pid_t ds_pid; /* [I] PID of tracing program */
void *ds_si; /* [I] to defer wakeup(9) */
- struct mutex ds_mtx;
-
struct dt_pcb_list ds_pcbs; /* [K] list of enabled PCBs */
int ds_recording; /* [K] currently recording? */
- int ds_evtcnt; /* [m] # of readable evts */
+ unsigned int ds_evtcnt; /* [a] # of readable evts */
+
+ struct dt_ringbuf ds_ring[MAXCPUS]; /* [I] event rings */
+ unsigned int ds_lastcpu; /* [r] last CPU ring read(2). */
/* Counters */
- uint64_t ds_readevt; /* [m] # of events read */
- uint64_t ds_dropevt; /* [m] # of events dropped */
+ unsigned int ds_readevt; /* [a] # of events read */
+ unsigned int ds_dropevt; /* [a] # of events dropped */
};
SLIST_HEAD(, dt_softc) dtdev_list; /* [K] list of open /dev/dt nodes */
@@ -142,7 +163,7 @@ int dt_ioctl_probe_enable(struct dt_softc *, struct dtioc_req *);
int dt_ioctl_probe_disable(struct dt_softc *, struct dtioc_req *);
int dt_ioctl_get_auxbase(struct dt_softc *, struct dtioc_getaux *);
-int dt_pcb_ring_copy(struct dt_pcb *, struct uio *, size_t, size_t *,
+int dt_ring_copy(struct dt_ringbuf *, struct uio *, size_t, size_t *,
uint64_t *);
void dt_wakeup(struct dt_softc *);
@@ -167,7 +188,8 @@ int
dtopen(dev_t dev, int flags, int mode, struct proc *p)
{
struct dt_softc *sc;
- int unit = minor(dev);
+ struct dt_evt *dtev;
+ int i, unit = minor(dev);
if (atomic_load_int(&allowdt) == 0)
return EPERM;
@@ -176,16 +198,31 @@ dtopen(dev_t dev, int flags, int mode, struct proc *p)
if (sc == NULL)
return ENOMEM;
- /* no sleep after this point */
if (dtlookup(unit) != NULL) {
free(sc, M_DEVBUF, sizeof(*sc));
return EBUSY;
}
+ for (i = 0; i < ncpusfound; i++) {
+ dtev = mallocarray(DT_EVTRING_SIZE, sizeof(*dtev), M_DT,
+ M_WAITOK|M_CANFAIL|M_ZERO);
+ if (dtev == NULL)
+ break;
+ sc->ds_ring[i].dr_ring = dtev;
+ }
+ if (i < ncpusfound) {
+ for (i--; i >= 0; i--) {
+ dtev = sc->ds_ring[i].dr_ring;
+ free(dtev, M_DT, DT_EVTRING_SIZE * sizeof(*dtev));
+ }
+ free(sc, M_DEVBUF, sizeof(*sc));
+ return ENOMEM;
+ }
+
sc->ds_unit = unit;
sc->ds_pid = p->p_p->ps_pid;
TAILQ_INIT(&sc->ds_pcbs);
- mtx_init(&sc->ds_mtx, IPL_HIGH);
+ sc->ds_lastcpu = 0;
sc->ds_evtcnt = 0;
sc->ds_readevt = 0;
sc->ds_dropevt = 0;
@@ -206,7 +243,8 @@ int
dtclose(dev_t dev, int flags, int mode, struct proc *p)
{
struct dt_softc *sc;
- int unit = minor(dev);
+ struct dt_evt *dtev;
+ int i, unit = minor(dev);
sc = dtlookup(unit);
KASSERT(sc != NULL);
@@ -218,6 +256,10 @@ dtclose(dev_t dev, int flags, int mode, struct proc *p)
dt_pcb_purge(&sc->ds_pcbs);
softintr_disestablish(sc->ds_si);
+ for (i = 0; i < ncpusfound; i++) {
+ dtev = sc->ds_ring[i].dr_ring;
+ free(dtev, M_DT, DT_EVTRING_SIZE * sizeof(*dtev));
+ }
free(sc, M_DEVBUF, sizeof(*sc));
return 0;
@@ -227,8 +269,8 @@ int
dtread(dev_t dev, struct uio *uio, int flags)
{
struct dt_softc *sc;
- struct dt_pcb *dp;
- int error = 0, unit = minor(dev);
+ struct dt_ringbuf *dr;
+ int i, error = 0, unit = minor(dev);
size_t count, max, read = 0;
uint64_t dropped = 0;
@@ -239,9 +281,9 @@ dtread(dev_t dev, struct uio *uio, int flags)
if (max < 1)
return (EMSGSIZE);
- while (!sc->ds_evtcnt) {
+ while (!atomic_load_int(&sc->ds_evtcnt)) {
sleep_setup(sc, PWAIT | PCATCH, "dtread");
- error = sleep_finish(0, !sc->ds_evtcnt);
+ error = sleep_finish(0, !atomic_load_int(&sc->ds_evtcnt));
if (error == EINTR || error == ERESTART)
break;
}
@@ -249,9 +291,10 @@ dtread(dev_t dev, struct uio *uio, int flags)
return error;
KERNEL_ASSERT_LOCKED();
- TAILQ_FOREACH(dp, &sc->ds_pcbs, dp_snext) {
+ for (i = 0; i < ncpusfound; i++) {
count = 0;
- error = dt_pcb_ring_copy(dp, uio, max, &count, &dropped);
+ dr = &sc->ds_ring[(sc->ds_lastcpu + i) % ncpusfound];
+ error = dt_ring_copy(dr, uio, max, &count, &dropped);
if (error && count == 0)
break;
@@ -260,12 +303,11 @@ dtread(dev_t dev, struct uio *uio, int flags)
if (max == 0)
break;
}
+ sc->ds_lastcpu += i % ncpusfound;
- mtx_enter(&sc->ds_mtx);
- sc->ds_evtcnt -= read;
- sc->ds_readevt += read;
- sc->ds_dropevt += dropped;
- mtx_leave(&sc->ds_mtx);
+ atomic_add_int(&sc->ds_readevt, read);
+ atomic_add_int(&sc->ds_dropevt, dropped);
+ atomic_sub_int(&sc->ds_evtcnt, read);
return error;
}
@@ -434,10 +476,8 @@ dt_ioctl_get_args(struct dt_softc *sc, struct dtioc_arg *dtar)
int
dt_ioctl_get_stats(struct dt_softc *sc, struct dtioc_stat *dtst)
{
- mtx_enter(&sc->ds_mtx);
- dtst->dtst_readevt = sc->ds_readevt;
- dtst->dtst_dropevt = sc->ds_dropevt;
- mtx_leave(&sc->ds_mtx);
+ dtst->dtst_readevt = atomic_load_int(&sc->ds_readevt);
+ dtst->dtst_dropevt = atomic_load_int(&sc->ds_dropevt);
return 0;
}
@@ -637,28 +677,16 @@ dt_pcb_alloc(struct dt_probe *dtp, struct dt_softc *sc)
dp = malloc(sizeof(*dp), M_DT, M_WAITOK|M_CANFAIL|M_ZERO);
if (dp == NULL)
- goto bad;
+ return NULL;
- dp->dp_ring = mallocarray(DT_EVTRING_SIZE, sizeof(*dp->dp_ring), M_DT,
- M_WAITOK|M_CANFAIL|M_ZERO);
- if (dp->dp_ring == NULL)
- goto bad;
-
- mtx_init(&dp->dp_mtx, IPL_HIGH);
dp->dp_sc = sc;
dp->dp_dtp = dtp;
return dp;
-bad:
- dt_pcb_free(dp);
- return NULL;
}
void
dt_pcb_free(struct dt_pcb *dp)
{
- if (dp == NULL)
- return;
- free(dp->dp_ring, M_DT, DT_EVTRING_SIZE * sizeof(*dp->dp_ring));
free(dp, M_DT, sizeof(*dp));
}
@@ -681,21 +709,26 @@ dt_pcb_ring_get(struct dt_pcb *dp, int profiling)
{
struct proc *p = curproc;
struct dt_evt *dtev;
- int distance;
+ int prod, cons, distance;
+ struct dt_ringbuf *dr = &dp->dp_sc->ds_ring[cpu_number()];
- mtx_enter(&dp->dp_mtx);
- distance = dp->dp_prod - dp->dp_cons;
+ dr->dr_block = splhigh();
+ membar_consumer();
+ prod = dr->dr_prod;
+ cons = dr->dr_cons;
+ distance = prod - cons;
if (distance == 1 || distance == (1 - DT_EVTRING_SIZE)) {
+ splx(dr->dr_block);
+
/* read(2) isn't finished */
- dp->dp_dropevt++;
- mtx_leave(&dp->dp_mtx);
+ atomic_inc_int(&dr->dr_dropevt);
return NULL;
}
/*
* Save states in next free event slot.
*/
- dtev = &dp->dp_ring[dp->dp_cons];
+ dtev = &dr->dr_ring[cons];
memset(dtev, 0, sizeof(*dtev));
dtev->dtev_pbn = dp->dp_dtp->dtp_pbn;
@@ -722,25 +755,27 @@ dt_pcb_ring_get(struct dt_pcb *dp, int profiling)
void
dt_pcb_ring_consume(struct dt_pcb *dp, struct dt_evt *dtev)
{
- MUTEX_ASSERT_LOCKED(&dp->dp_mtx);
- KASSERT(dtev == &dp->dp_ring[dp->dp_cons]);
+ struct dt_ringbuf *dr = &dp->dp_sc->ds_ring[cpu_number()];
- dp->dp_cons = (dp->dp_cons + 1) % DT_EVTRING_SIZE;
- mtx_leave(&dp->dp_mtx);
+ KASSERT(dtev == &dr->dr_ring[dr->dr_cons]);
+
+ dr->dr_cons = (dr->dr_cons + 1) % DT_EVTRING_SIZE;
+ membar_producer();
+
+ splx(dr->dr_block);
+
+ atomic_inc_int(&dp->dp_sc->ds_evtcnt);
- mtx_enter(&dp->dp_sc->ds_mtx);
- dp->dp_sc->ds_evtcnt++;
- mtx_leave(&dp->dp_sc->ds_mtx);
dt_wakeup(dp->dp_sc);
}
/*
- * Copy at most `max' events from `dp', producing the same amount
+ * Copy at most `max' events from `dr', producing the same amount
* of free slots.
*/
int
-dt_pcb_ring_copy(struct dt_pcb *dp, struct uio *uio, size_t max,
- size_t *rcvd, uint64_t *dropped)
+dt_ring_copy(struct dt_ringbuf *dr, struct uio *uio, size_t max,
+ size_t *rcvd, uint64_t *dropped)
{
size_t count, copied = 0;
unsigned int cons, prod;
@@ -748,12 +783,10 @@ dt_pcb_ring_copy(struct dt_pcb *dp, struct uio *uio, size_t max,
KASSERT(max > 0);
- mtx_enter(&dp->dp_mtx);
- cons = dp->dp_cons;
- prod = dp->dp_prod;
- *dropped += dp->dp_dropevt;
- dp->dp_dropevt = 0;
- mtx_leave(&dp->dp_mtx);
+ membar_consumer();
+ cons = dr->dr_cons;
+ prod = dr->dr_prod;
+ *dropped += atomic_swap_uint(&dr->dr_dropevt, 0);
if (cons < prod)
count = DT_EVTRING_SIZE - prod;
@@ -764,7 +797,7 @@ dt_pcb_ring_copy(struct dt_pcb *dp, struct uio *uio, size_t max,
return 0;
count = MIN(count, max);
- error = uiomove(&dp->dp_ring[prod], count * sizeof(struct dt_evt), uio);
+ error = uiomove(&dr->dr_ring[prod], count * sizeof(struct dt_evt), uio);
if (error)
return error;
copied += count;
@@ -777,7 +810,7 @@ dt_pcb_ring_copy(struct dt_pcb *dp, struct uio *uio, size_t max,
goto out;
count = MIN(cons, (max - copied));
- error = uiomove(&dp->dp_ring[0], count * sizeof(struct dt_evt), uio);
+ error = uiomove(&dr->dr_ring[0], count * sizeof(struct dt_evt), uio);
if (error)
goto out;
@@ -785,9 +818,8 @@ dt_pcb_ring_copy(struct dt_pcb *dp, struct uio *uio, size_t max,
prod += count;
out:
- mtx_enter(&dp->dp_mtx);
- dp->dp_prod = prod;
- mtx_leave(&dp->dp_mtx);
+ dr->dr_prod = prod;
+ membar_producer();
*rcvd = copied;
return error;
diff --git a/sys/dev/dt/dtvar.h b/sys/dev/dt/dtvar.h
index 5bb7ab0d7715..07e2b6c2f6df 100644
--- a/sys/dev/dt/dtvar.h
+++ b/sys/dev/dt/dtvar.h
@@ -163,12 +163,6 @@ struct dt_pcb {
SMR_SLIST_ENTRY(dt_pcb) dp_pnext; /* [K,S] next PCB per probe */
TAILQ_ENTRY(dt_pcb) dp_snext; /* [K] next PCB per softc */
- /* Event states ring */
- unsigned int dp_prod; /* [m] read index */
- unsigned int dp_cons; /* [m] write index */
- struct dt_evt *dp_ring; /* [m] ring of event states */
- struct mutex dp_mtx;
-
struct dt_softc *dp_sc; /* [I] related softc */
struct dt_probe *dp_dtp; /* [I] related probe */
uint64_t dp_evtflags; /* [I] event states to record */
@@ -177,9 +171,6 @@ struct dt_pcb {
struct clockintr dp_clockintr; /* [D] profiling handle */
uint64_t dp_nsecs; /* [I] profiling period */
struct cpu_info *dp_cpu; /* [I] on which CPU */
-
- /* Counters */
- uint64_t dp_dropevt; /* [m] # dropped event */
};
TAILQ_HEAD(dt_pcb_list, dt_pcb);
dt: Use one ringbuffer per CPU