[dpdk-stable] [dpdk-dev] [PATCH v3 1/3] ring: read tail using atomic load

[Ola Liljedahl]

On 08/10/2018, 16:44, "Bruce Richardson" <bruce.richardson at intel.com> wrote:

    On Mon, Oct 08, 2018 at 09:22:05AM +0000, Ola Liljedahl wrote:
    <snip> 
    > "* multi-producer safe lock-free ring buffer enqueue"
    > The comment is also wrong. This design is not lock-free, how could it be when there is spinning
    > (waiting) for other threads in the code? If a thread must wait for other threads, then by definition
    > the design is blocking.
    >
    My understanding is that the code is lock-free but not wait-free, though
    I'm not an expert in this area.
Notice this code:
	while (br->br_cons_tail != cons_head)
		cpu_spinwait();
Waiting for another thread to update a specific location => blocking.
Sure, the code doesn't use locks but that doesn't make it lock-free (in the computer science meaning).


    
    /Bruce