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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-01-25 14:28:28 -0500
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-02-26 14:57:29 -0500
commitc25197841efe53258abb22cfd894a729a272edf9 (patch)
tree2aee40a0447d3380378b9d0e77148c3a015c352f /Documentation/timers
parent89bf5d82ed451f02329bbbb06ac365e96b18804d (diff)
documentation: Update NO_HZ_FULL interaction with POSIX timers
POSIX timers are no longer starved on adaptive-ticks CPUs. Instead, they prevent affected CPUs from entering adaptive-ticks mode. This commit therefore updates the NO_HZ.txt documentation. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/timers')
-rw-r--r--Documentation/timers/NO_HZ.txt10
1 files changed, 3 insertions, 7 deletions
diff --git a/Documentation/timers/NO_HZ.txt b/Documentation/timers/NO_HZ.txt
index cca122f25120..6eaf576294f3 100644
--- a/Documentation/timers/NO_HZ.txt
+++ b/Documentation/timers/NO_HZ.txt
@@ -158,13 +158,9 @@ not come for free:
158 to the need to inform kernel subsystems (such as RCU) about 158 to the need to inform kernel subsystems (such as RCU) about
159 the change in mode. 159 the change in mode.
160 160
1613. POSIX CPU timers on adaptive-tick CPUs may miss their deadlines 1613. POSIX CPU timers prevent CPUs from entering adaptive-tick mode.
162 (perhaps indefinitely) because they currently rely on 162 Real-time applications needing to take actions based on CPU time
163 scheduling-tick interrupts. This will likely be fixed in 163 consumption need to use other means of doing so.
164 one of two ways: (1) Prevent CPUs with POSIX CPU timers from
165 entering adaptive-tick mode, or (2) Use hrtimers or other
166 adaptive-ticks-immune mechanism to cause the POSIX CPU timer to
167 fire properly.
168 164
1694. If there are more perf events pending than the hardware can 1654. If there are more perf events pending than the hardware can
170 accommodate, they are normally round-robined so as to collect 166 accommodate, they are normally round-robined so as to collect