Virtualization and Linux on a DSP Processor

A small tidbit that I found interesting due to the targeted platform. LinuxDevices reports that the VirtualLogix VLX-NI virtualization layer that used to run only on x86 platforms now also run on TI DSPs in the C64+ series. Basically, you put their virtualization layer on the DSP, and you can then on the same core run both a Linux kernel and a DSP/BIOS kernel. Thus supporting traditional DSP development and Linux-style development on the same core.

On x86, the virtualization uses the virtualization extensions in recent editions of Intel and AMD processors. There is no such support on the C64+ DSP series, so they fall back to paravirtualization, modifying the operating systems to play nice with the virtualization layer. Nothing particularly magical about this.

The interesting part is really that people are considering using Linux which is usually very hard to tune for non-standard hardware platforms to run code on a real high-power DSP. In general, that is considered a bad idea since what you want is a thin layer of software to let you do compute programs that make maximum use of the processor. Doing interrupts and other typical OS work on a DSP is a bad idea since it breaks program flow. Some instructions sequences on a C64-type DSP even require you to turn off interrupts in order to work correctly! So I guess the performance of Linux programs are going to be pretty poor… However, the idea here seems to be to move some control-plane functions onto the DSPs in the system, which is going to be poorly performing code anyway.  I guess it makes sense if you have spare cycles on the DSP to be able to do away with the additional control-plane processor (which is usually a small slow processor anyway on the kind of base station software being targeted here).

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