sd-event: try to move timer wakeups to the same spot within each minute

[elogind.git] / src / libsystemd-bus / sd-event.c

diff --git a/src/libsystemd-bus/sd-event.c b/src/libsystemd-bus/sd-event.c
index 2dc3672142680998584deae9c539aacba32723f4..2a8eac6df2fdd3cb9401250f7affb41ec45f80d5 100644 (file)
--- a/src/libsystemd-bus/sd-event.c
+++ b/src/libsystemd-bus/sd-event.c
@@ -640,15 +640,16 @@ static int event_setup_timer_fd(
         }
 
         /* When we sleep for longer, we try to realign the wakeup to
         }
 
         /* When we sleep for longer, we try to realign the wakeup to

-           the same time wihtin each second, so that events all across
-           the system can be coalesced into a single CPU
-           wakeup. However, let's take some system-specific randomness
-           for this value, so that in a network of systems with synced
-           clocks timer events are distributed a bit. Here, we
-           calculate a perturbation usec offset from the boot ID. */
+           the same time wihtin each minute/second/250ms, so that
+           events all across the system can be coalesced into a single
+           CPU wakeup. However, let's take some system-specific
+           randomness for this value, so that in a network of systems
+           with synced clocks timer events are distributed a
+           bit. Here, we calculate a perturbation usec offset from the
+           boot ID. */

 
         if (sd_id128_get_boot(&bootid) >= 0)
 
         if (sd_id128_get_boot(&bootid) >= 0)

-                e->perturb = (bootid.qwords[0] ^ bootid.qwords[1]) % USEC_PER_SEC;
+                e->perturb = (bootid.qwords[0] ^ bootid.qwords[1]) % USEC_PER_MINUTE;

 
         *timer_fd = fd;
         return 0;
 
         *timer_fd = fd;
         return 0;


@@ -1363,13 +1364,24 @@ static usec_t sleep_between(sd_event *e, usec_t a, usec_t b) {
              dispatch as much as possible on the entire system.
 
           We implement this by waking up everywhere at the same time
              dispatch as much as possible on the entire system.
 
           We implement this by waking up everywhere at the same time

-          within any given second if we can, synchronised via the
+          within any given minute if we can, synchronised via the

           perturbation value determined from the boot ID. If we can't,
           perturbation value determined from the boot ID. If we can't,

-          then we try to find the same spot in every a 250ms
+          then we try to find the same spot in every 1s and then 250ms

           step. Otherwise, we pick the last possible time to wake up.
         */
 
           step. Otherwise, we pick the last possible time to wake up.
         */
 

-        c = (b / USEC_PER_SEC) * USEC_PER_SEC + e->perturb;
+        c = (b / USEC_PER_MINUTE) * USEC_PER_MINUTE + e->perturb;
+        if (c >= b) {
+                if (_unlikely_(c < USEC_PER_MINUTE))
+                        return b;
+
+                c -= USEC_PER_MINUTE;
+        }
+
+        if (c >= a)
+                return c;
+
+        c = (b / USEC_PER_SEC) * USEC_PER_SEC + (e->perturb % USEC_PER_SEC);

         if (c >= b) {
                 if (_unlikely_(c < USEC_PER_SEC))
                         return b;
         if (c >= b) {
                 if (_unlikely_(c < USEC_PER_SEC))
                         return b;