Add a new cmpxchg interface:
bool try_cmpxchg(u{8,16,32,64} *ptr, u{8,16,32,64} *val, u{8,16,32,64} new);
Where the boolean returns the result of the compare; and thus if the
exchange happened; and in case of failure, the new value of *ptr is
returned in *val.
This allows simplification/improvement of loops like:
for (;;) {
new = val $op $imm;
old = cmpxchg(ptr, val, new);
if (old == val)
break;
val = old;
}
into:
do {
} while (!try_cmpxchg(ptr, &val, val $op $imm));
while also generating better code (GCC6 and onwards).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
a9ebf306f5