On Tue, 21 Mar 2017 20:13:48 -0400 Ed Czeck <ed.cz...@atomicrules.com> wrote:
> Hi Stephen, > > Yes I understand the paranoid issue of volatile modifier, which is the > reason it was coded in this manner. > > The struct with volatile are memory mapped IO structures. These structure > are not instantiated in memory and hence do not incur concurrent (host) > software access. The a vast majority of the fields as read-only (as viewed > by the host.) The concurrency model is that hardware is the producer, and > the host the consumer. There is no handshake other than the host must not > expect the memory location to remain constant -- that is optimization off. > > As for performance, these structures are not in any critical path, so he > optimization path is correctness not performance. > > Do you have a recommendation for changing this code without using the > volatile modifier? I have requirements from the hardware in the pattern of: > write a 1 to location x > read from location y until it become 0 > write a 0 to location x > How can this work without a volatile modified on x and y? > > Best, > Ed. Learn to use explicit memory barriers. DPDK has rmb()/wmb() just like kernel. Once again good explanation of memory barriers in kernel doc.
