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documentation: Update NO_HZ_FULL interaction with POSIX timers

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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>
This commit is contained in:
Paul E. McKenney 2015-01-25 11:28:28 -08:00
parent 89bf5d82ed
commit c25197841e
1 changed files with 3 additions and 7 deletions
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Documentation/timers/NO_HZ.txt
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@ -158,13 +158,9 @@ not come for free:
to the need to inform kernel subsystems (such as RCU) about
the change in mode.
3. POSIX CPU timers on adaptive-tick CPUs may miss their deadlines
(perhaps indefinitely) because they currently rely on
scheduling-tick interrupts. This will likely be fixed in
one of two ways: (1) Prevent CPUs with POSIX CPU timers from
entering adaptive-tick mode, or (2) Use hrtimers or other
adaptive-ticks-immune mechanism to cause the POSIX CPU timer to
fire properly.
3. POSIX CPU timers prevent CPUs from entering adaptive-tick mode.
Real-time applications needing to take actions based on CPU time
consumption need to use other means of doing so.
4. If there are more perf events pending than the hardware can
accommodate, they are normally round-robined so as to collect