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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-10-09 15:13:11 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-12-11 10:31:40 -0800
commit0c53dd8b31404c1d7fd15be8f065ebaec615a562 (patch)
treea12d5ced107fed7a6cdc3a82525d328de9b9d9f3 /Documentation/RCU/whatisRCU.txt
parenta7b152d5342c06e81ab0cf7d18345f69fa7e56b5 (diff)
downloadlinux-linaro-stable-0c53dd8b31404c1d7fd15be8f065ebaec615a562.tar.gz
rcu: Introduce raw SRCU read-side primitives
The RCU implementations, including SRCU, are designed to be used in a lock-like fashion, so that the read-side lock and unlock primitives must execute in the same context for any given read-side critical section. This constraint is enforced by lockdep-RCU. However, there is a need to enter an SRCU read-side critical section within the context of an exception and then exit in the context of the task that encountered the exception. The cost of this capability is that the read-side operations incur the overhead of disabling interrupts. Note that although the current implementation allows a given read-side critical section to be entered by one task and then exited by another, all known possible implementations that allow this have scalability problems. Therefore, a given read-side critical section must be exited by the same task that entered it, though perhaps from an interrupt or exception handler running within that task's context. But if you are thinking in terms of interrupt handlers, make sure that you have considered the possibility of threaded interrupt handlers. Credit goes to Peter Zijlstra for suggesting use of the existing _raw suffix to indicate disabling lockdep over the earlier "bulkref" names. Requested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
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