This patch set implements the "big hammer" expedited RCU grace periods. This leverages the existing per-CPU migration kthreads, as suggested by Ingo. These are awakened in a loop, and waited for in a second loop. Not fully scalable, but removing the extra hop through smp_call_function reduces latency on systems with moderate numbers of CPUs. The synchronize_rcu_expedited() and synchronize_bh_expedited() primitives invoke synchronize_sched_expedited(), except for CONFIG_PREEMPT_RCU, where they instead invoke synchronize_rcu() and synchronize_rcu_bh(), respectively. This will be fixed in the future, after preemptable RCU is folded into the rcutree implementation. As before, this does nothing to expedite callbacks already registered with call_rcu() or call_rcu_bh(), but there is no need to. Passes many hours of rcutorture testing in parallel with a script that randomly offlines and onlines CPUs in a number of configurations. Grace periods take about 40 microseconds on an 8-CPU Power machine, which I believe is good enough from a performance viewpoint for the near future. This represents some slowdown from v7, which was unfortunately necessary to fix some bugs. This is finally ready for inclusion. ;-) Shortcomings: o Does not address preemptable RCU (though synchronize_sched_expedited() is in fact expedited in this configuration). o Probably not helpful on systems with thousands of CPUs, but likely quite helpful even on systems with a few hundred CPUs. Changes since v7: o Fixed several embarrassing bugs turned up by tests on multiple configurations. Changes since v6: o Moved to using the migration threads, as suggested by Ingo. Changes since v5: o Fixed several embarrassing locking bugs, including those noted by Ingo and Lai. o Added a missing set of braces. o Cut out the extra kthread, so that synchronize_sched_expedited() directly calls smp_call_function() and waits for the quiescent states. o Removed some debug code, but promoted one to production. o Fix a compiler warning. Changes since v4: o Use per-CPU kthreads to force the quiescent states in parallel. Changes since v3: o Use a kthread that schedules itself on each CPU in turn to force a grace period. The synchronize_rcu() primitive wakes up the kthread in order to avoid messing with affinity masks on user tasks. o Tried a number of additional variations on the v3 approach, none of which helped much. Changes since v2: o Use reschedule IPIs rather than a softirq. Changes since v1: o Added rcutorture support, and added exports required by rcutorture. o Added comment stating that smp_call_function() implies a memory barrier, suggested by Mathieu. o Added #include for delay.h. Documentation/RCU/torture.txt | 17 +++ include/linux/rcuclassic.h | 15 ++- include/linux/rcupdate.h | 25 ++--- include/linux/rcupreempt.h | 10 ++ include/linux/rcutree.h | 12 ++ kernel/rcupdate.c | 25 +++++ kernel/rcutorture.c | 202 ++++++++++++++++++++++-------------------- kernel/sched.c | 129 ++++++++++++++++++++++++++ 8 files changed, 327 insertions(+), 108 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
