From 0412acb95ffac94d5916ee19991cc7194e55953c Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Tue, 13 Nov 2018 12:48:49 +0100

Subject: [PATCH] core: make sure we don't throttle change signal generator

 when a reload is pending

Fixes: #10627

(cherry picked from commit b8d381c47776ea0440af175cbe0c02cb743bde08)

Resolves: #1647359

---

 src/core/manager.c | 64 ++++++++++++++++++++++++++++------------------

 1 file changed, 39 insertions(+), 25 deletions(-)

diff --git a/src/core/manager.c b/src/core/manager.c

index a24bfcacd..3b2fe11e8 100644

--- a/src/core/manager.c

+++ b/src/core/manager.c

@@ -2074,56 +2074,70 @@ static unsigned manager_dispatch_dbus_queue(Manager *m) {

         assert(m);

+        /* Avoid recursion */

         if (m->dispatching_dbus_queue)

                 return 0;

-        /* Anything to do at all? */

-        if (!m->dbus_unit_queue && !m->dbus_job_queue && !m->send_reloading_done && !m->pending_reload_message)

-                return 0;

+        /* When we are reloading, let's not wait with generating signals, since we need to exit the manager as quickly

+         * as we can. There's no point in throttling generation of signals in that case. */

+        if (MANAGER_IS_RELOADING(m) || m->send_reloading_done || m->pending_reload_message)

+                budget = (unsigned) -1; /* infinite budget in this case */

+        else {

+                /* Anything to do at all? */

+                if (!m->dbus_unit_queue && !m->dbus_job_queue)

+                        return 0;

-        /* Do we have overly many messages queued at the moment? If so, let's not enqueue more on top, let's sit this

-         * cycle out, and process things in a later cycle when the queues got a bit emptier. */

-        if (manager_bus_n_queued_write(m) > MANAGER_BUS_BUSY_THRESHOLD)

-                return 0;

+                /* Do we have overly many messages queued at the moment? If so, let's not enqueue more on top, let's

+                 * sit this cycle out, and process things in a later cycle when the queues got a bit emptier. */

+                if (manager_bus_n_queued_write(m) > MANAGER_BUS_BUSY_THRESHOLD)

+                        return 0;

-        /* Only process a certain number of units/jobs per event loop iteration. Even if the bus queue wasn't overly

-         * full before this call we shouldn't increase it in size too wildly in one step, and we shouldn't monopolize

-         * CPU time with generating these messages. Note the difference in counting of this "budget" and the

-         * "threshold" above: the "budget" is decreased only once per generated message, regardless how many

-         * busses/direct connections it is enqueued on, while the "threshold" is applied to each queued instance of bus

-         * message, i.e. if the same message is enqueued to five busses/direct connections it will be counted five

-         * times. This difference in counting ("references" vs. "instances") is primarily a result of the fact that

-         * it's easier to implement it this way, however it also reflects the thinking that the "threshold" should put

-         * a limit on used queue memory, i.e. space, while the "budget" should put a limit on time. Also note that

-         * the "threshold" is currently chosen much higher than the "budget". */

-        budget = MANAGER_BUS_MESSAGE_BUDGET;

+                /* Only process a certain number of units/jobs per event loop iteration. Even if the bus queue wasn't

+                 * overly full before this call we shouldn't increase it in size too wildly in one step, and we

+                 * shouldn't monopolize CPU time with generating these messages. Note the difference in counting of

+                 * this "budget" and the "threshold" above: the "budget" is decreased only once per generated message,

+                 * regardless how many busses/direct connections it is enqueued on, while the "threshold" is applied to

+                 * each queued instance of bus message, i.e. if the same message is enqueued to five busses/direct

+                 * connections it will be counted five times. This difference in counting ("references"

+                 * vs. "instances") is primarily a result of the fact that it's easier to implement it this way,

+                 * however it also reflects the thinking that the "threshold" should put a limit on used queue memory,

+                 * i.e. space, while the "budget" should put a limit on time. Also note that the "threshold" is

+                 * currently chosen much higher than the "budget". */

+                budget = MANAGER_BUS_MESSAGE_BUDGET;

+        }

         m->dispatching_dbus_queue = true;

-        while (budget > 0 && (u = m->dbus_unit_queue)) {

+        while (budget != 0 && (u = m->dbus_unit_queue)) {

                 assert(u->in_dbus_queue);

                 bus_unit_send_change_signal(u);

-                n++, budget--;

+                n++;

+

+                if (budget != (unsigned) -1)

+                        budget--;

         }

-        while (budget > 0 && (j = m->dbus_job_queue)) {

+        while (budget != 0 && (j = m->dbus_job_queue)) {

                 assert(j->in_dbus_queue);

                 bus_job_send_change_signal(j);

-                n++, budget--;

+                n++;

+

+                if (budget != (unsigned) -1)

+                        budget--;

         }

         m->dispatching_dbus_queue = false;

-        if (budget > 0 && m->send_reloading_done) {

+        if (m->send_reloading_done) {

                 m->send_reloading_done = false;

                 bus_manager_send_reloading(m, false);

-                n++, budget--;

+                n++;

         }

-        if (budget > 0 && m->pending_reload_message) {

+        if (m->pending_reload_message) {

                 bus_send_pending_reload_message(m);

                 n++;

         }