On 2012/1/17 22:57, John Baldwin wrote:
> On Monday, January 16, 2012 1:15:14 am David Xu wrote:
>> Author: davidxu
>> Date: Mon Jan 16 06:15:14 2012
>> New Revision: 230201
>> URL: http://svn.freebsd.org/changeset/base/230201
>>
>> Log:
>> Insert read memory barriers.
> I think using atomic_load_acq() on sem->nwaiters would be clearer as it would
> indicate which variable you need to ensure is read after other operations. In
> general I think raw rmb/wmb usage should be avoided when possible as it is
> does not describe the programmer's intent as well.
>
Yes, I had considered that I may use atomic_load_acq(), but at that time,
I thought it emits a bus locking, right ? so I just picked up rmb() which
only affects current cpu. maybe atomic_load_acq() does same thing with
rmb() ?
it is still unclear to me.
Regards,
David Xu