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From 2a0feeb4252cbf1207f45e978fe7eb02bb0182ec Mon Sep 17 00:00:00 2001
From: Kyle Walker <walker.kyle.t@gmail.com>
Date: Thu, 30 Jun 2016 15:12:18 -0400
Subject: [PATCH] manager: Only invoke a single sigchld per unit within a
cleanup cycle
By default, each iteration of manager_dispatch_sigchld() results in a unit level
sigchld event being invoked. For scope units, this results in a scope_sigchld_event()
which can seemingly stall for workloads that have a large number of PIDs within the
scope. The stall exhibits itself as a SIG_0 being initiated for each u->pids entry
as a result of pid_is_unwaited().
v2:
This patch resolves this condition by only paying to cost of a sigchld in the underlying
scope unit once per sigchld iteration. A new "sigchldgen" member resides within the
Unit struct. The Manager is incremented via the sd event loop, accessed via
sd_event_get_iteration, and the Unit member is set to the same value as the manager each
time that a sigchld event is invoked. If the Manager iteration value and Unit member
match, the sigchld event is not invoked for that iteration.
Cherry-picked from: 36f20ae3b2975e44b6ef17e453ae06a289e9a122
Resolves: #1342173
---
src/core/manager.c | 13 ++++++++++++-
src/core/unit.c | 1 +
src/core/unit.h | 3 +++
3 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/src/core/manager.c b/src/core/manager.c
index e5226a8a6..63693b93a 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -1747,14 +1747,25 @@ static int manager_dispatch_notify_fd(sd_event_source *source, int fd, uint32_t
}
static void invoke_sigchld_event(Manager *m, Unit *u, siginfo_t *si) {
+ uint64_t iteration;
+
assert(m);
assert(u);
assert(si);
+ sd_event_get_iteration(m->event, &iteration);
+
log_unit_debug(u->id, "Child "PID_FMT" belongs to %s", si->si_pid, u->id);
unit_unwatch_pid(u, si->si_pid);
- UNIT_VTABLE(u)->sigchld_event(u, si->si_pid, si->si_code, si->si_status);
+
+ if (UNIT_VTABLE(u)->sigchld_event) {
+ if (set_size(u->pids) <= 1 || iteration != u->sigchldgen) {
+ UNIT_VTABLE(u)->sigchld_event(u, si->si_pid, si->si_code, si->si_status);
+ u->sigchldgen = iteration;
+ } else
+ log_debug("%s already issued a sigchld this iteration %llu, skipping. Pids still being watched %d", u->id, iteration, set_size(u->pids));
+ }
}
static int manager_dispatch_sigchld(Manager *m) {
diff --git a/src/core/unit.c b/src/core/unit.c
index d6ead7d67..d62135d87 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -94,6 +94,7 @@ Unit *unit_new(Manager *m, size_t size) {
u->unit_file_state = _UNIT_FILE_STATE_INVALID;
u->unit_file_preset = -1;
u->on_failure_job_mode = JOB_REPLACE;
+ u->sigchldgen = 0;
return u;
}
diff --git a/src/core/unit.h b/src/core/unit.h
index 0eebc0b89..d93645777 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -167,6 +167,9 @@ struct Unit {
* process SIGCHLD for */
Set *pids;
+ /* Used in sigchld event invocation to avoid repeat events being invoked */
+ uint64_t sigchldgen;
+
/* Used during GC sweeps */
unsigned gc_marker;