Linux netmap memory allocation

[Charlie Smurthwaite]

Hi,

I'm just starting to use netmap and it is my intention to do zero-copy
forwarding of frames between a large number of NICs. I am using Intel
i350 (igb) on Linux. I therefore require a large memory area for rings
and buffers.

My calculation:
32 NICs * 2 rings (TX+RX) * 256 frames * 2048 bytes = 32MB

I am currently having a problem (or perhaps just a misunderstanding)
regarding allocation of this memory. I am attempting to use the
following code:

void thread_main(int thread_id) {
   struct nmreq req; // A struct for the netmap request
   int fd;           // File descriptor for netmap socket
   void * mem;       // Pointer to allocated memory area

   fd = open("/dev/netmap", 0);     // Open a generic netmap socket
   strcpy(req.nr_name, "enp8s0f0"); // Copy NIC name into request
   req.nr_version = NETMAP_API;     // Set version number
   req.nr_flags = NR_REG_ONE_NIC;   // We will be using a single hw ring

   // Select ring 0, disable TX on poll
   req.nr_ringid = NETMAP_NO_TX_POLL | NETMAP_HW_RING | 0;

   // Ask for 64 additional rings to be allocated (32 * (TX+RX))
   req.nr_arg1 = 64;

   // Allocate a separate memory area for each thread
   req.nr_arg2 = 10 + thread_id;

   // Ask for additional buffers (256 per ring)
   req.nr_arg3 = 64*256;

   // Initialize port
   ioctl(fd, NIOCREGIF, &req);

   // Check the allocated memory size
   printf("memsize: %u\n", req.nr_memsize);
   // Check the allocated memory area
   printf("nr_arg2: %u\n", req.nr_arg2);
}

The output is as follows:

memsize: 4206859
nr_arg2: 10

This is far short of the amount of memory I am hoping to be allocated.
Am I doing something wrong, or is this simply an indication that the
driver is unwilling to allocate more than 4MB?

A secondary (related) problem is that if I don't set arg1,arg2,arg3 in
my code (ie they will be zero), then I get varying output (it varies
between each of the following):

memsize: 4206843
nr_arg2: 0

memsize: 343019520
nr_arg2: 1

Any pointers would be appreciated. Thanks!

Charlie


Charlie Smurthwaite
Technical Director

tel.  email. charlie at atech.media<mailto:charlie at atech.media> web. https://atech.media

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