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authorIngo Molnar <mingo@elte.hu>2009-07-03 19:56:36 +0200
committerIngo Molnar <mingo@elte.hu>2009-07-03 20:23:55 +0200
commit3a8d1788b37435baf6c296f4ea8beb4fa4955f44 (patch)
tree0db4ee093c0d9c8cb66321945fc024e5b1d3a8fd /arch/x86/lib
parent1fde902d52ee13ab9fab155bbae757fdf7daf0c1 (diff)
downloadop-kernel-dev-3a8d1788b37435baf6c296f4ea8beb4fa4955f44.zip
op-kernel-dev-3a8d1788b37435baf6c296f4ea8beb4fa4955f44.tar.gz
x86: atomic64: Improve atomic64_xchg()
Remove the read-first logic from atomic64_xchg() and simplify the loop. This function was the last user of __atomic64_read() - remove it. Also, change the 'real_val' assumption from the somewhat quirky 1ULL << 32 value to the (just as arbitrary, but simpler) value of 0. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: David Howells <dhowells@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Arnd Bergmann <arnd@arndb.de> LKML-Reference: <tip-05118ab8859492ac9ddda0154cf90e37b0a4a0b0@git.kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/lib')
-rw-r--r--arch/x86/lib/atomic64_32.c21
1 files changed, 15 insertions, 6 deletions
diff --git a/arch/x86/lib/atomic64_32.c b/arch/x86/lib/atomic64_32.c
index 6722a09..a804f96 100644
--- a/arch/x86/lib/atomic64_32.c
+++ b/arch/x86/lib/atomic64_32.c
@@ -33,14 +33,23 @@ EXPORT_SYMBOL(atomic64_cmpxchg);
* Atomically xchgs the value of @ptr to @new_val and returns
* the old value.
*/
-
u64 atomic64_xchg(atomic64_t *ptr, u64 new_val)
{
- u64 old_val;
+ /*
+ * Try first with a (possibly incorrect) assumption about
+ * what we have there. We'll do two loops most likely,
+ * but we'll get an ownership MESI transaction straight away
+ * instead of a read transaction followed by a
+ * flush-for-ownership transaction:
+ */
+ u64 old_val, real_val = 0;
do {
- old_val = __atomic64_read(ptr);
- } while (atomic64_cmpxchg(ptr, old_val, new_val) != old_val);
+ old_val = real_val;
+
+ real_val = atomic64_cmpxchg(ptr, old_val, new_val);
+
+ } while (real_val != old_val);
return old_val;
}
@@ -91,13 +100,13 @@ EXPORT_SYMBOL(atomic64_read);
noinline u64 atomic64_add_return(u64 delta, atomic64_t *ptr)
{
/*
- * Try first with a (probably incorrect) assumption about
+ * Try first with a (possibly incorrect) assumption about
* what we have there. We'll do two loops most likely,
* but we'll get an ownership MESI transaction straight away
* instead of a read transaction followed by a
* flush-for-ownership transaction:
*/
- u64 old_val, new_val, real_val = 1ULL << 32;
+ u64 old_val, new_val, real_val = 0;
do {
old_val = real_val;
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