[dpdk-dev] Possible bug in eal_pci pci_scan_one

[Matthew Hall <mhall@mhcomputing.net>]

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.