lkml.org 
[lkml]   [2016]   [Apr]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][PATCH 3/3] locking,arm64: Introduce cmpwait()
On Sat, Apr 23, 2016 at 12:08:57AM +0800, Boqun Feng wrote:
> On Tue, Apr 12, 2016 at 05:59:41PM +0100, Will Deacon wrote:
> [...]
> > > +static inline void __cmpwait(volatile void *ptr, unsigned long val, int size)
> > > +{
> > > + switch (size) {
> > > + case 1: return __cmpwait_case_1(ptr, val);
> > > + case 2: return __cmpwait_case_2(ptr, val);
> > > + case 4: return __cmpwait_case_4(ptr, val);
> > > + case 8: return __cmpwait_case_8(ptr, val);
> > > + default: BUILD_BUG();
> > > + }
> > > +
> > > + unreachable();
> > > +}
> > > +
> > > +#define cmpwait(ptr, val) \
> > > + __cmpwait((ptr), (unsigned long)(val), sizeof(*(ptr)))
> >
> > We might want to call this cmpwait_relaxed, in case we decide to add
> > fenced versions in the future. Or just make it cmpwait_acquire and
> > remove the smp_rmb() from smp_cond_load_acquire(). Dunno.
> >
>
> How about replace smp_rmb() with a smp_acquire_barrier__after_cmpwait()?
> This barrier is designed to provide an ACQUIRE ordering when combining a
> cmpwait() .
>
> And cmpwait() only has minimal ordering guarantee, but if it is actually
> an ACQUIRE, then the corresponding smp_acquire_barrier__after_cmpwait()
> is just empty.

Maybe, but that makes it difficult for me to use a load-acquire instruction
for the ACQUIRE case.

Will

\
 
 \ /
  Last update: 2016-04-22 19:21    [W:0.122 / U:0.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site