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Diffstat (limited to 'Documentation/percpu-rw-semaphore.txt')
| -rw-r--r-- | Documentation/percpu-rw-semaphore.txt | 27 |
1 files changed, 0 insertions, 27 deletions
diff --git a/Documentation/percpu-rw-semaphore.txt b/Documentation/percpu-rw-semaphore.txt deleted file mode 100644 index 7d3c82431909..000000000000 --- a/Documentation/percpu-rw-semaphore.txt +++ /dev/null @@ -1,27 +0,0 @@ -Percpu rw semaphores --------------------- - -Percpu rw semaphores is a new read-write semaphore design that is -optimized for locking for reading. - -The problem with traditional read-write semaphores is that when multiple -cores take the lock for reading, the cache line containing the semaphore -is bouncing between L1 caches of the cores, causing performance -degradation. - -Locking for reading is very fast, it uses RCU and it avoids any atomic -instruction in the lock and unlock path. On the other hand, locking for -writing is very expensive, it calls synchronize_rcu() that can take -hundreds of milliseconds. - -The lock is declared with "struct percpu_rw_semaphore" type. -The lock is initialized percpu_init_rwsem, it returns 0 on success and --ENOMEM on allocation failure. -The lock must be freed with percpu_free_rwsem to avoid memory leak. - -The lock is locked for read with percpu_down_read, percpu_up_read and -for write with percpu_down_write, percpu_up_write. - -The idea of using RCU for optimized rw-lock was introduced by -Eric Dumazet <eric.dumazet@gmail.com>. -The code was written by Mikulas Patocka <mpatocka@redhat.com> |