AW: Shared Umem between processes

["Gaul, Maximilian" <maximilian.gaul@hm.edu>]

I don't know if it is appropriate to ask a new question on the same topic in the same thread? In case it is not I will start a new one but I thought it would fit "my story on how to get shared umem working".

I followed https://github.com/xdp-project/bpf-next/blob/master/samples/bpf/xdpsock_user.c on how to implement shared umem and I think I got it working to some extend.

There are some problems though:

I am processing two multicast streams arriving on the same RX-Queue on two sockets (using shared umem) - each socket is running in its own thread (same process).
What I noticed: Everything seems to work fine for about 1min or so (even though I am noticing some packet-loss for 530.000 pps) but after that, datarate drops to only half and after one more minute to a fourth.

My first thought on this was that the reserved umem frames by calling `xsk_ring_prod__reserve` are not freed properly (similiar to a memory leak) because of that I decreased the size of the umem to a tenth hoping to see a decrease in packet rate even sooner - and indeed I did!

Basically what I do is to create a new thread for each socket and pass the `xsk_socket_info`-struct accordingly. I then call `nanosleep` for 2.5ms in a while-loop and process every frame that arrived:

static void* rx_and_process(void *a) {

	struct pthread_arg *arg = (struct pthread_arg*)a;
	struct config *cfg = arg->cfg;
	struct pckt_idntfy_stats *pckt = arg->pckt_idntfy;
	struct xsk_socket_info *xsk_socket = arg->xsk_socket;

	struct timespec spec;
	spec.tv_sec = 0;
	spec.tv_nsec = 2500 * 1000;

	struct timespec remaining;

	while(!global_exit) {
		if(nanosleep(&spec, &remaining) < 0) {
			nanosleep(&spec, &remaining);
		}
		handle_receive_packets(xsk_socket, fds);
	}

	return NULL;
}

`pckt_idntfy_stats` contains information about where the statistics about this multicast-stream should be placed in shared memory.

Processing then happens like this:

static void handle_receive_packets(struct xsk_socket_info *xsk_socket, struct pollfd *fds) {
	unsigned int rcvd, i;
	uint32_t idx_rx = 0, idx_fq = 0;
	int ret;

	rcvd = xsk_ring_cons__peek(&xsk_socket->rx, INT32_MAX, &idx_rx);
	if (!rcvd) {
        /* no packets received, go to sleep */
		return;
	}

	ret = xsk_ring_prod__reserve(&xsk_socket->umem->fq, rcvd, &idx_fq);
	if (ret < 0) {
		fprintf(stderr, "Error: %s\n", strerror(-ret));
		return;
	} else if(ret == 0) {
		printf("NO SPACE LEFT!\n");
		return;
	} else if(ret != rcvd) {
		printf("RET != RCVD\n");
		return;
	}

	for (i = 0; i < rcvd; i++) {
		uint64_t addr = xsk_ring_cons__rx_desc(&xsk_socket->rx, idx_rx)->addr;
		uint32_t len = xsk_ring_cons__rx_desc(&xsk_socket->rx, idx_rx++)->len;
		uint64_t orig = xsk_umem__extract_addr(addr);

		addr = xsk_umem__add_offset_to_addr(addr);

		process_packet(xsk_socket, addr, len);
		*xsk_ring_prod__fill_addr(&xsk_socket->umem->fq, idx_fq++) = orig;
		
		xsk_socket->stats.rx_bytes += len;
	}

	xsk_ring_prod__submit(&xsk_socket->umem->fq, rcvd);
	xsk_ring_cons__release(&xsk_socket->rx, rcvd);
	xsk_socket->stats.rx_packets += rcvd;
}

I am sorry to post all this code here but maybe it helps?

This is how I configured the umem (basically a 1:1 copy from `xdpsock_user.c`:

static struct xsk_umem_info *configure_xsk_umem(void *buffer, uint64_t size) {

	struct xsk_umem_info *umem;
	struct xsk_umem_config cfg = {
		.fill_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
		.comp_size = XSK_RING_CONS__DEFAULT_NUM_DESCS,
		.frame_size = FRAME_SIZE,
		.frame_headroom = XSK_UMEM__DEFAULT_FRAME_HEADROOM,
		.flags = 0
	};
	int ret;

	umem = calloc(1, sizeof(*umem));
	if (!umem) {
		fprintf(stderr, "Error while allocating umem: %s\n", strerror(errno));
		exit(1);
	}

	ret = xsk_umem__create(&umem->umem, buffer, size, &umem->fq, &umem->cq, &cfg);
	if (ret) {
		fprintf(stderr, "`xsk_umem__create` returned: %s\n", strerror(-ret));
		exit(1);
	}

	umem->buffer = buffer;
	return umem;
}

and after that I call:

static void xsk_populate_fill_ring(struct xsk_umem_info *umem) {
	int ret, i;
	uint32_t idx;

	ret = xsk_ring_prod__reserve(&umem->fq, XSK_RING_PROD__DEFAULT_NUM_DESCS, &idx);
	if (ret != XSK_RING_PROD__DEFAULT_NUM_DESCS) {
		fprintf(stderr, "Failed to reserve prod ring: %s\n", strerror(errno));
		exit(1);
	}
	for (i = 0; i < XSK_RING_PROD__DEFAULT_NUM_DESCS; i++) {
		*xsk_ring_prod__fill_addr(&umem->fq, idx++) = i * FRAME_SIZE;
	}
	xsk_ring_prod__submit(&umem->fq, XSK_RING_PROD__DEFAULT_NUM_DESCS);
}

And sockets are created this way:

static struct xsk_socket_info *xsk_configure_socket(struct xsk_umem_info *umem, struct config *cfg, bool rx, bool tx) {
	struct xsk_socket_config xsk_socket_cfg;
 	struct xsk_socket_info *xsk;
	struct xsk_ring_cons *rxr;
	struct xsk_ring_prod *txr;
	int ret;

	xsk = calloc(1, sizeof(*xsk));
	if (!xsk) {
		fprintf(stderr, "xsk `calloc` failed: %s\n", strerror(errno));
		exit(1);
	}

	xsk->umem = umem;
	xsk_socket_cfg.rx_size = XSK_RING_CONS__DEFAULT_NUM_DESCS;
	xsk_socket_cfg.tx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS;
	if (cfg->ip_addrs_len > 1) {
		xsk_socket_cfg.libbpf_flags = XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD;
	} else {
		xsk_socket_cfg.libbpf_flags = 0;
	}
	xsk_socket_cfg.xdp_flags = cfg->xdp_flags;
	xsk_socket_cfg.bind_flags = cfg->xsk_bind_flags;

	rxr = rx ? &xsk->rx : NULL;
	txr = tx ? &xsk->tx : NULL;
	ret = xsk_socket__create(&xsk->xsk, cfg->ifname_buf, cfg->xsk_if_queue, umem->umem, rxr, txr, &xsk_socket_cfg);
	if (ret) {
		fprintf(stderr, "`xsk_socket__create` returned error: %s\n", strerror(errno));
		exit(-ret);
	}

	return xsk;
}

As far as I've seen from `xdpsock_user.c` there is no special handling required by the sockets who are using shared umem? What am I missing?

Best regards

Max