File 0176-erts-Scheduler-pollset-migration-only-when-single-pr.patch of Package erlang
From c89cbee31536fa5897a74f4d8e0e2d8bde860a6d Mon Sep 17 00:00:00 2001
From: Andrew Bennett <potatosaladx@meta.com>
Date: Thu, 23 Oct 2025 14:50:48 -0500
Subject: [PATCH] [erts] Scheduler pollset migration only when single process
enif_select
---
erts/emulator/sys/common/erl_check_io.c | 40 +++++++++++++++++++------
1 file changed, 31 insertions(+), 9 deletions(-)
diff --git a/erts/emulator/sys/common/erl_check_io.c b/erts/emulator/sys/common/erl_check_io.c
index 7f87ed57d2..3914e003a7 100644
--- a/erts/emulator/sys/common/erl_check_io.c
+++ b/erts/emulator/sys/common/erl_check_io.c
@@ -200,6 +200,7 @@ typedef struct {
EventStateFlags flags;
int count; /* Number of times this fd has triggered
without being deselected. */
+ Eterm last_select_pid; /* Last process that called enif_select */
} ErtsDrvEventState;
struct drv_ev_state_shared {
@@ -290,6 +291,7 @@ static ERTS_INLINE int grow_drv_ev_state(ErtsSysFdType fd) {
sizeof(ErtsDrvEventState) * (new_len - old_len));
for (i = old_len; i < new_len; i++) {
drv_ev_state.v[i].fd = (ErtsSysFdType) i;
+ drv_ev_state.v[i].last_select_pid = NIL;
}
erts_atomic_set_nob(&drv_ev_state.len, new_len);
for (i=0; i<ERTS_CHECK_IO_DRV_EV_STATE_LOCK_CNT; i++) {
@@ -333,6 +335,8 @@ static ERTS_INLINE ErtsDrvEventState* new_drv_ev_state(ErtsDrvEventState *state,
tmpl.active_events = 0;
tmpl.type = ERTS_EV_TYPE_NONE;
tmpl.flags = 0;
+ tmpl.count = 0;
+ tmpl.last_select_pid = NIL;
return (ErtsDrvEventState *) safe_hash_put(&drv_ev_state.tab, (void *) &tmpl);
}
@@ -922,6 +926,7 @@ deselect(ErtsDrvEventState *state, int mode)
state->type = ERTS_EV_TYPE_NONE;
state->flags = ERTS_EV_FLAG_CLEAR;
state->count = 0;
+ state->last_select_pid = NIL;
} else {
ErtsPollEvents new_events =
erts_io_control(state, ERTS_POLL_OP_MOD, state->active_events);
@@ -1248,6 +1253,7 @@ enif_select_x(ErlNifEnv* env,
ErtsDrvSelectDataState *free_select = NULL;
ErtsNifSelectDataState *free_nif = NULL;
ErtsPollEvents new_events = 0;
+ const Eterm recipient = pid ? pid->pid : env->proc->common.id;
#ifdef DEBUG_PRINT_MODE
char tmp_buff[255];
#endif
@@ -1340,15 +1346,24 @@ enif_select_x(ErlNifEnv* env,
old_events = state->events;
if (on) {
+ ASSERT(is_internal_pid(recipient));
+
if (state->type == ERTS_EV_TYPE_NONE)
ctl_op = ERTS_POLL_OP_ADD;
#if ERTS_POLL_USE_SCHEDULER_POLLING
- else {
- if (!(state->flags & ERTS_EV_FLAG_SCHEDULER) &&
- !(state->flags & ERTS_EV_FLAG_FALLBACK) &&
- (ctl_events & ERTS_POLL_EV_IN)) {
- if (erts_sched_poll_enabled() && (state->flags & ERTS_EV_FLAG_NIF_SELECT) &&
- state->count++ > 10) {
+ else if (ctl_events & ERTS_POLL_EV_IN) {
+ if ((state->flags & (ERTS_EV_FLAG_SCHEDULER |
+ ERTS_EV_FLAG_FALLBACK |
+ ERTS_EV_FLAG_NIF_SELECT)) == ERTS_EV_FLAG_NIF_SELECT
+ && erts_sched_poll_enabled()) {
+ /* Check if this is a different process than last time.
+ * If so, reset the counter to prevent scheduler pollset migration
+ * in multi-process scenarios (e.g., multiple socket:accept callers). */
+ if (state->last_select_pid != recipient) {
+ state->count = 0;
+ state->last_select_pid = recipient;
+ }
+ else if (++(state->count) > 10) {
int wake_poller = 0;
DEBUG_PRINT_FD("moving to scheduler ps", state);
new_events = erts_poll_control(get_scheduler_pollset(), fd, ERTS_POLL_OP_ADD,
@@ -1359,7 +1374,7 @@ enif_select_x(ErlNifEnv* env,
old_events = state->events;
}
}
- if (ctl_events & ERTS_POLL_EV_IN) {
+ {
ErtsSchedulerData *esdp = erts_get_scheduler_data();
erts_io_clear_nif_select(fd, state);
/* Clear the marker in scheduler data so that the scheduler
@@ -1408,6 +1423,8 @@ enif_select_x(ErlNifEnv* env,
if (state->type == ERTS_EV_TYPE_NIF && !old_events) {
state->type = ERTS_EV_TYPE_NONE;
state->flags = 0;
+ state->count = 0;
+ state->last_select_pid = NIL;
state->driver.nif->in.pid = NIL;
state->driver.nif->out.pid = NIL;
state->driver.nif->err.pid = NIL;
@@ -1421,8 +1438,6 @@ enif_select_x(ErlNifEnv* env,
|| state->type == ERTS_EV_TYPE_NONE);
if (on) {
- const Eterm recipient = pid ? pid->pid : env->proc->common.id;
- ASSERT(is_internal_pid(recipient));
if (!state->driver.nif)
state->driver.nif = alloc_nif_select_data();
if (state->type == ERTS_EV_TYPE_NONE) {
@@ -1497,6 +1512,7 @@ enif_select_x(ErlNifEnv* env,
ret |= ERL_NIF_SELECT_STOP_SCHEDULED;
}
state->count = 0;
+ state->last_select_pid = NIL;
state->flags &= ~ERTS_EV_FLAG_WANT_ERROR;
}
else
@@ -1777,6 +1793,8 @@ steal_pending_stop_use(erts_dsprintf_buf_t *dsbufp, ErlDrvPort ix,
}
state->type = ERTS_EV_TYPE_NONE;
state->flags = 0;
+ state->count = 0;
+ state->last_select_pid = NIL;
state->driver.stop.drv_ptr = NULL;
}
else {
@@ -1816,6 +1834,8 @@ steal_pending_stop_nif(erts_dsprintf_buf_t *dsbufp, ErtsResource* resource,
enif_release_resource(state->driver.stop.resource->data);
state->type = ERTS_EV_TYPE_NONE;
state->flags = 0;
+ state->count = 0;
+ state->last_select_pid = NIL;
state->driver.stop.resource = NULL;
}
else {
@@ -2014,6 +2034,7 @@ erts_check_io(ErtsPollThread *psi, ErtsMonotonicTime timeout_time, int poll_only
erts_poll_control(get_scheduler_pollset(), fd, ERTS_POLL_OP_DEL, 0, &wake_poller);
state->flags &= ~(ERTS_EV_FLAG_SCHEDULER|ERTS_EV_FLAG_IN_SCHEDULER);
state->count = 0;
+ state->last_select_pid = NIL;
}
#endif
} else {
@@ -2034,6 +2055,7 @@ erts_check_io(ErtsPollThread *psi, ErtsMonotonicTime timeout_time, int poll_only
state->flags &= ~(ERTS_EV_FLAG_IN_SCHEDULER|ERTS_EV_FLAG_SCHEDULER);
state->active_events &= ~ERTS_POLL_EV_IN;
state->count = 0;
+ state->last_select_pid = NIL;
}
} else
#endif
--
2.51.0
