Possible bug in eal_pci pci_scan_one

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.

Hi,

Did anybody get a chance to look what might be going on in this weird NUMA bug? I could use some help to understand how you're supposed to make code that will work right on both NUMA and non-NUMA. Otherwise it's hard to make a bulletproof DPDK based app that will be able to reliably init on single socket, dual socket non-NUMA, and dual socket NUMA boxes.

Thanks,
Matthew.

Quoted 63 lines · Matthew Hall

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.

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.