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| author | Paul E. McKenney <paul.mckenney@linaro.org> | 2011-11-28 12:28:34 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-12-11 10:32:07 -0800 |
| commit | 7cb92499000e3c86dae653077b1465458a039ef6 (patch) | |
| tree | ebc982a5cc562b4fe0cb8f20541f45a5506a0b5f /include/trace | |
| parent | 3842a0832a1d6eb0b31421f8810a813135967512 (diff) | |
| download | blackbird-obmc-linux-7cb92499000e3c86dae653077b1465458a039ef6.tar.gz blackbird-obmc-linux-7cb92499000e3c86dae653077b1465458a039ef6.zip | |
rcu: Permit dyntick-idle with callbacks pending
The current implementation of RCU_FAST_NO_HZ prevents CPUs from entering
dyntick-idle state if they have RCU callbacks pending. Unfortunately,
this has the side-effect of often preventing them from entering this
state, especially if at least one other CPU is not in dyntick-idle state.
However, the resulting per-tick wakeup is wasteful in many cases: if the
CPU has already fully responded to the current RCU grace period, there
will be nothing for it to do until this grace period ends, which will
frequently take several jiffies.
This commit therefore permits a CPU that has done everything that the
current grace period has asked of it (rcu_pending() == 0) even if it
still as RCU callbacks pending. However, such a CPU posts a timer to
wake it up several jiffies later (6 jiffies, based on experience with
grace-period lengths). This wakeup is required to handle situations
that can result in all CPUs being in dyntick-idle mode, thus failing
to ever complete the current grace period. If a CPU wakes up before
the timer goes off, then it cancels that timer, thus avoiding spurious
wakeups.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'include/trace')
| -rw-r--r-- | include/trace/events/rcu.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 8dd6fcb94946..c75418c3ccb8 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -288,9 +288,10 @@ TRACE_EVENT(rcu_dyntick, * "No callbacks": Nothing to do, no callbacks on this CPU. * "In holdoff": Nothing to do, holding off after unsuccessful attempt. * "Begin holdoff": Attempt failed, don't retry until next jiffy. + * "Dyntick with callbacks": Entering dyntick-idle despite callbacks. * "More callbacks": Still more callbacks, try again to clear them out. * "Callbacks drained": All callbacks processed, off to dyntick idle! - * "CPU awakened at GP end": + * "Timer": Timer fired to cause CPU to continue processing callbacks. */ TRACE_EVENT(rcu_prep_idle, |
