linux-kernel - [PATCH 1/3] locking/percpu-rwsem: Move text file into Documentation/locking/

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Message-Id: <1479495277-9075-2-git-send-email-dave@stgolabs.net>
Date:   Fri, 18 Nov 2016 10:54:35 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     mingo@...nel.org, peterz@...radead.org, oleg@...hat.com
Cc:     john.stultz@...aro.org, dimitrysh@...gle.com,
        linux-kernel@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 1/3] locking/percpu-rwsem: Move text file into Documentation/locking/

Although this is rather useless and the actual code is orders
of magnitude more detailed and informative than this document.

Might as well keep it instead, I guess its already there and
could give a user a quick why/when use them vs regular rwsems.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 Documentation/locking/percpu-rw-semaphore.txt | 27 +++++++++++++++++++++++++++
 Documentation/percpu-rw-semaphore.txt         | 27 ---------------------------
 2 files changed, 27 insertions(+), 27 deletions(-)
 create mode 100644 Documentation/locking/percpu-rw-semaphore.txt
 delete mode 100644 Documentation/percpu-rw-semaphore.txt

diff --git a/Documentation/locking/percpu-rw-semaphore.txt b/Documentation/locking/percpu-rw-semaphore.txt
new file mode 100644
index 000000000000..7d3c82431909
--- /dev/null
+++ b/Documentation/locking/percpu-rw-semaphore.txt
@@ -0,0 +1,27 @@
+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@...il.com>.
+The code was written by Mikulas Patocka <mpatocka@...hat.com>
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@...il.com>.
-The code was written by Mikulas Patocka <mpatocka@...hat.com>
-- 
2.6.6