On 07/24/2015 01:16 PM, Frederic Weisbecker wrote:
On Fri, Jul 24, 2015 at 12:55:35PM -0400, Chris Metcalf wrote:
On 07/23/2015 12:42 PM, Frederic Weisbecker wrote:
+unsigned long __tick_nohz_set_tick_dependency(enum tick_dependency_bit bit,
+ unsigned long *dep)
+{
+ unsigned long prev;
+ unsigned long old = *dep;
+ unsigned long mask = BIT_MASK(bit);
+
+ while ((prev = cmpxchg(dep, old, old | mask)) != old) {
+ old = prev;
+ cpu_relax();
+ }
+
+ return prev;
+}
Why not use set_bit() here? It is suitably atomic.
Because I don't want to send an IPI if the CPU already had bits set in
the dependency.
Ideally I need something like test_and_set_bit() but which returns the
whole previous value and not just the previous value of the bit.
Ah, of course. Peter, maybe we need atomic_or_return() as part
of your new atomic_or/_and/_xor series? Certainly on tilegx, and
likely other architectures, we can do better than Frederic's
cmpxchg() loop.
--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com
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