MFC r316342, r316358

r316342:
Consolidate random sleeps in periodic scripts

Multiple periodic scripts sleep for a random amount of time in order to
mitigate the thundering herd problem. This is bad, because the sum of
multiple uniformly distributed random variables approaches a normal
distribution, so the problem isn't mitigated as effectively as it would be
with a single sleep.

This change creates a single configurable anticongestion sleep. periodic
will only sleep if at least one script requires it, and it will never sleep
more than once per invocation. It also won't sleep if periodic was run
interactively, fixing an unrelated longstanding bug.

PR:		217055
PR:		210188
Reviewed by:	cy
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D10211

r316358:
Fix man page typo from r316342

Reported by:	rgrimes
MFC after:	20 days
X-MFC-With:	316342

1 files changed, 5 insertions, 1 deletions

diff --git a/share/man/man5/periodic.conf.5 b/share/man/man5/periodic.conf.5
index cb9a8b0..cd56745 100644
--- a/share/man/man5/periodic.conf.5
+++ b/share/man/man5/periodic.conf.5
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 26, 2015
+.Dd March 31, 2017
 .Dt PERIODIC.CONF 5
 .Os
 .Sh NAME
@@ -133,6 +133,10 @@ respectively.
 Refer to the
 .Xr periodic 8
 manual page for how script return codes are interpreted.
+.It Va anticongestion_sleeptime
+.Pq Vt int
+The maximum number of seconds to randomly sleep in order to smooth bursty loads
+on a shared resource, such as a download mirror.
 .El
 .Pp
 The following variables are used by the standard scripts that reside in