Messages in this thread Patch in this message | | | Date | Fri, 3 Jul 2009 18:30:47 GMT | From | tip-bot for Ingo Molnar <> | Subject | [tip:perfcounters/urgent] x86: atomic64: Improve atomic64_xchg() |
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Commit-ID: 3a8d1788b37435baf6c296f4ea8beb4fa4955f44 Gitweb: http://git.kernel.org/tip/3a8d1788b37435baf6c296f4ea8beb4fa4955f44 Author: Ingo Molnar <mingo@elte.hu> AuthorDate: Fri, 3 Jul 2009 19:56:36 +0200 Committer: Ingo Molnar <mingo@elte.hu> CommitDate: Fri, 3 Jul 2009 20:23:55 +0200
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>
--- arch/x86/include/asm/atomic_32.h | 9 --------- arch/x86/lib/atomic64_32.c | 21 +++++++++++++++------ 2 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/arch/x86/include/asm/atomic_32.h b/arch/x86/include/asm/atomic_32.h index aa045de..d7c8849 100644 --- a/arch/x86/include/asm/atomic_32.h +++ b/arch/x86/include/asm/atomic_32.h @@ -268,15 +268,6 @@ typedef struct { #define ATOMIC64_INIT(val) { (val) } -/** - * atomic64_read - read atomic64 variable - * @ptr: pointer of type atomic64_t - * - * Atomically reads the value of @v. - * Doesn't imply a read memory barrier. - */ -#define __atomic64_read(ptr) ((ptr)->counter) - extern u64 atomic64_cmpxchg(atomic64_t *ptr, u64 old_val, u64 new_val); /** 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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