Original Link: http://www.anandtech.com/show/6380/boston-viridis-arm-server-gets-x86-binary-translation-support

We covered the launch of the Calxeda-based Boston Viridis ARM server back in July. The server is makings its appearance at the UK IP EXPO 2012. Boston has been blogging about their work on the Viridis over the last few months, and one of the most interesting aspects is the fact that x86 binary translation now works on the Viridis. The technology is from Eltech, and they have apparently given the seal of approval to the Calxeda platform by indicating that the Boston Viridis was the fastest platform they had tested.

Eltech seems to be doing dynamic binary translation, i.e, x86 binaries are translated on the fly. That makes the code a bit bulky (heavier on the I-Cache). The overhead is relatively large compared to, say, VMware's binary translator (BT) that does x86 to x86, becauseof the necessity to translate between two different ISAs.

Eltech uses a 1 MB translator cache (similar to the translator cache of VMware's BT), which means they can reuse earlier translations. The translation overhead will thus decrease quickly over time if most of the critical loops fit in the translator cache. But it also means that only code with a relatively small footprint will run fast, e.g. get the promised 40-65% of native performance.

Most server applications have a relatively large instruction memory footprint, so it is unclear whether this approach will help to run any heavy server software. Some HPC softwares have a small memory footprint, but since the HPC users tend to pursue performance most of the time, this technology is unlikely to convince them to use ARM servers instead of x86.

In general, the BT software will be useful in the - not uncommon - case where one may have a complex web application comprised of multiple software modules where one small piece of software is not open-source and the vendor does not offer an ARM based binary. So, the Eltech solution does handle a small piece of the puzzle. x86 emulation is thus a nice to have feature, but most ARM based servers will be running fully optimized and recompiled linux software.  That is the target market for products such as the Boston Viridis. 

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