X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=blobdiff_plain;f=Documentation%2Fspinlocks.txt;h=9dbe885ecd8d130e8a1e0300f05686dea59440c6;hp=2e3c64b1a6a5a64ede63c9e76377f79514e95088;hb=75b56ec294b074d70f8a676ab02611a3fea76cab;hpb=adff377bb1010ec65aada1f94ef2be7c7805c711

diff --git a/Documentation/spinlocks.txt b/Documentation/spinlocks.txt
index 2e3c64b1a6a5..9dbe885ecd8d 100644
--- a/Documentation/spinlocks.txt
+++ b/Documentation/spinlocks.txt
@@ -13,18 +13,8 @@ static DEFINE_SPINLOCK(xxx_lock);
 The above is always safe. It will disable interrupts _locally_, but the
 spinlock itself will guarantee the global lock, so it will guarantee that
 there is only one thread-of-control within the region(s) protected by that
-lock. This works well even under UP. The above sequence under UP
-essentially is just the same as doing
-
-	unsigned long flags;
-
-	save_flags(flags); cli();
-	 ... critical section ...
-	restore_flags(flags);
-
-so the code does _not_ need to worry about UP vs SMP issues: the spinlocks
-work correctly under both (and spinlocks are actually more efficient on
-architectures that allow doing the "save_flags + cli" in one operation).
+lock. This works well even under UP also, so the code does _not_ need to
+worry about UP vs SMP issues: the spinlocks work correctly under both.
 
    NOTE! Implications of spin_locks for memory are further described in:
 
@@ -36,27 +26,7 @@ The above is usually pretty simple (you usually need and want only one
 spinlock for most things - using more than one spinlock can make things a
 lot more complex and even slower and is usually worth it only for
 sequences that you _know_ need to be split up: avoid it at all cost if you
-aren't sure). HOWEVER, it _does_ mean that if you have some code that does
-
-	cli();
-	.. critical section ..
-	sti();
-
-and another sequence that does
-
-	spin_lock_irqsave(flags);
-	.. critical section ..
-	spin_unlock_irqrestore(flags);
-
-then they are NOT mutually exclusive, and the critical regions can happen
-at the same time on two different CPU's. That's fine per se, but the
-critical regions had better be critical for different things (ie they
-can't stomp on each other).
-
-The above is a problem mainly if you end up mixing code - for example the
-routines in ll_rw_block() tend to use cli/sti to protect the atomicity of
-their actions, and if a driver uses spinlocks instead then you should
-think about issues like the above.
+aren't sure).
 
 This is really the only really hard part about spinlocks: once you start
 using spinlocks they tend to expand to areas you might not have noticed
@@ -120,11 +90,10 @@ Lesson 3: spinlocks revisited.
 
 The single spin-lock primitives above are by no means the only ones. They
 are the most safe ones, and the ones that work under all circumstances,
-but partly _because_ they are safe they are also fairly slow. They are
-much faster than a generic global cli/sti pair, but slower than they'd
-need to be, because they do have to disable interrupts (which is just a
-single instruction on a x86, but it's an expensive one - and on other
-architectures it can be worse).
+but partly _because_ they are safe they are also fairly slow. They are slower
+than they'd need to be, because they do have to disable interrupts
+(which is just a single instruction on a x86, but it's an expensive one -
+and on other architectures it can be worse).
 
 If you have a case where you have to protect a data structure across
 several CPU's and you want to use spinlocks you can potentially use