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[PATCH] mutex subsystem, documentation

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Add mutex design related documentation.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
This commit is contained in:
Ingo Molnar
2006-01-09 15:59:20 -08:00
committed by Ingo Molnar
parent 6053ee3b32
commit f3f54ffa70
2 changed files with 149 additions and 8 deletions
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22
Documentation/DocBook/kernel-locking.tmpl
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@ -222,7 +222,7 @@
<title>Two Main Types of Kernel Locks: Spinlocks and Semaphores</title>
<para>
There are two main types of kernel locks. The fundamental type
There are three main types of kernel locks. The fundamental type
is the spinlock
(<filename class="headerfile">include/asm/spinlock.h</filename>),
which is a very simple single-holder lock: if you can't get the
@ -230,16 +230,22 @@
very small and fast, and can be used anywhere.
</para>
<para>
The second type is a semaphore
The second type is a mutex
(<filename class="headerfile">include/linux/mutex.h</filename>): it
is like a spinlock, but you may block holding a mutex.
If you can't lock a mutex, your task will suspend itself, and be woken
up when the mutex is released. This means the CPU can do something
else while you are waiting. There are many cases when you simply
can't sleep (see <xref linkend="sleeping-things"/>), and so have to
use a spinlock instead.
</para>
<para>
The third type is a semaphore
(<filename class="headerfile">include/asm/semaphore.h</filename>): it
can have more than one holder at any time (the number decided at
initialization time), although it is most commonly used as a
single-holder lock (a mutex). If you can't get a semaphore,
your task will put itself on the queue, and be woken up when the
semaphore is released. This means the CPU will do something
else while you are waiting, but there are many cases when you
simply can't sleep (see <xref linkend="sleeping-things"/>), and so
have to use a spinlock instead.
single-holder lock (a mutex). If you can't get a semaphore, your
task will be suspended and later on woken up - just like for mutexes.
</para>
<para>
Neither type of lock is recursive: see