So, it would take an existing radio source (Flash, ICY, MMS, etc), transcode the codec and format to suite the listener, and when it detected ad spots select and insert a targeted ad. slices), etc.įor example, for a startup, I implemented a real-time streaming radio transcoder which inserted targeted, per-listener, dynamically selected ad spots into live streams. I use tools like Ragel, lean fifo buffers in C with moving read and write windows (i.e. I've had success simply reducing the number of data copies in userspace. I never went down the rabbit hole of zero-copy, only watched various teams crash and burn. If most of what you care about is avoiding the cost of the kernel/userspace split, then you can just use NetBSD Rump or similar unikernel frameworks. The exception to this state of affairs is when they're doing read-only packet sniffing and filtering, simply passing the packets back out another interface. All the weirdness, head scratching, and hair pulling these solutions cause is an externality engineers will never care about, and in most cases probably be oblivious about. And IMO the amazing throughput most people claim to see with DPDK is a result of simply neglecting to implement all the hard logic which makes the Internet actually work. At the same time you're now responsible for all of that. I think the real benefit of DPDK and netmap is that you're avoiding all the logic of the existing IP stacks, not to mention firewall rules, etc. Both can do DMA with user space buffers with much less disruption to traditional design patterns for implementing network daemons. You can do zero copy I/O on Linux using vmsplice+extensions, and on FreeBSD using regular read/write calls. The gain in performance is significant, but I have no numbers at hand to give. Since dpdk and netmap communicates directly with the network card, it only works with supported network cards. Then there is dpdk on which I don't have much info yet except that it is made by Intel, it is open source and compatible with AMD processors. Zero copy is the future of network programming. It is not included in the Linux kernel and you then need to patch it in. My colleague told me that Netmap is available in the BSD kernel so that you can use it right away. At CERN they are now testing data acquisition setups using dpdk to be able to use commodity component hardware. My colleague is currently using netmap for a high performance data acquisition application in a LAN and plan to test dpdk with mTCP this summer. I was told that it can work with dpdk and netmap. So it's up to you to code and decode the TCP/IP headers or use an existing lib like mTCP that does that for you. This block contains raw network data received from the network card. Once you have a block you can process it. In the user space you use select/epoll/kqueue or polling if the waiting time is very small. When data arrives, it is directly written in place in a block of the memory mapped zone. I never used it so I don't know the details. Blocks have a fixed size big enough to hold the ~1500 IP blocks. This zone is organized as a pool of blocks managed with non blocking lists. The way it works, as I was explained, is that they use a shared memory mapped zone. The "zero copy" networking stacks avoids the data copy. Then your read operation copies that data in your user space. Normally, when the kernel recieves data from the network, it allocates a block in the kernel and copy the data into it. The core functionality required is a "zero copy" networking lib : dpdk, netmap.
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