On Mon, 6 Oct 2014 02:13:44 -0700
Matthew Hall <mhall at mhcomputing.net> wrote:
> Hi Guys,
>
> I'm doing my development on kind of a cheap machine with no NUMA support...
> but several years ago I used DPDK to build a NUMA box that could do 40 gbits
> bidirectional L4-L7 stateful traffic replay.
>
> So given the past experiences I had before, I wanted to clean the code up so
> it'd work well if some crazy guy tried my code on one of these huge boxes,
> too, but then I ran into some weird issues.
>
> 1) When I call rte_eth_dev_socket_id() I get back -1. But the call can return
> -1 if the port_id is bogus or if pci_scan_one didn't get a numa_node (because
> you're on a non-NUMA box for example).
>
> int rte_eth_dev_socket_id(uint8_t port_id)
> {
> if (port_id >= nb_ports)
> return -1;
> return rte_eth_devices[port_id].pci_dev->numa_node;
> }
>
> So you couldn't tell the different between non-NUMA or a bad port value, etc.
>
> 2) The code's behavior and comments disagree with one another. In the
> pci_scan_one function, there's this code:
>
> /* get numa node */
> snprintf(filename, sizeof(filename), "%s/numa_node",
> dirname);
> if (access(filename, R_OK) != 0) {
> /* if no NUMA support just set node to 0 */
> dev->numa_node = -1;
> } else {
> if (eal_parse_sysfs_value(filename, &tmp) < 0) {
> free(dev);
> return -1;
> }
> dev->numa_node = tmp;
> }
>
> It says, just use NUMA node 0 if there is no NUMA support. But then proceeds
> to set the value to -1 in disagreement with the comment, and also stomping on
> the other meaning for -1 in the higher function rte_eth_dev_socket_id.
>
> 3) In conclusion, it seems like some stuff is missing... first there needs to
> be a function that will tell you the number of NUMA nodes present on the box
> so you can create the right number of mbuf_pools, but I couldn't find that
> function.
>
> Then if you have the function, you can do some magic and shuffle the NICs
> around to get them hooked to a core on the same NUMA, and the mbuf_pool on
> the
> same NUMA.
>
> When NUMA is not present, can we return 0 instead of -1, or return a specific
> error code that the client can use to know he should just use Socket 0? Right
> now I can't tell apart any potential errors or weird values from correct
> values.
>
> 4) I'm willing to help make and test some patches... but first I want to
> understand what is happening with these funny functions before doing things
> blindly.
>
> Thanks,
> Matthew.
The code is fairly consistent in returning -1 for cases of not a NUMA socket,
bogus port value. It is interpreted as SOCKET_ID_ANY in several places.
The examples mostly check for -1 and use socket 0 as a fallback.
Probably not worth introducing more return values and breaking existing
applications.
