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ARM Readies Cores For 64-Bit Computing
snydeq writes "ARM Holdings will unveil new plans for processing cores that support 64-bit computing within the next few weeks, and has already shown samples at private viewings, InfoWorld reports. ARM's move to put out a 64-bit processing core will give its partners more options to design products for more markets, including servers, the source said. The next ARM Cortex processor to be unveiled will support 64-bit computing. An announcement of the processor could come as early as next week, and may provide further evidence of a collision course with Intel."
You don't see the use?
low-latency bare-metal fileservers that consume only a few watts, but can natively handle huge filesystems and live encryption? It's a lot easier to handle a multi-TB storage array when you're 64-bit native, same for encryption. Look at Linux benchmarks for 32 vs 64-bit filesystem and OpenSSH performance.
Do you have any idea how many $4,000 Intel Xeon boxes basically sit and do nothing all day at the average enterprise? If you can put Linux on these beasties, you could have a cheap and inexpensive place for projects to start, if load ever kills the 2GHz ARM blade, you can migrate the app over to an Intel VM or bare metal. I'll bet 80% of projects never leave the ARM boxes, though.
My whole department (currently seven bare-metal Intel servers and five VMs) could run entirely off of a few ARM boxes running Linux. It would probably save an employees'-worth of power, cooling, upkeep, and upgrade costs every year.
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n900 may be a nice device otherwise but only 256MB is totally crippling. Most recent smartphones come with 512MB these days. So even for just RAM, having merely "plans" about migrating to 64 bit today is not overkill, it's long overdue.
About your idea of just mmapping everything: the speed difference between memory and disk/flash is so big that the current split is pretty vital to a non-toy OS. I'd limit mmap to specific tasks, for which it is indeed underused.
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Look at Linux benchmarks for 32 vs 64-bit filesystem and OpenSSH performance
What benchmarks are you looking at? If you're comparing x86 to x86-64, then you are going to get some very misleading numbers. In addition to the increased address space, x86-64 gives:
Offsetting this is the fact that all pointers are now twice as big, which means that you use more instruction cache. On a more sane architecture, such as SPARC, PowerPC, or MIPS, you get none of these advantages (or, rather, removal of disadvantages), so 64-bit code generally runs slightly slower. The only reason to compile in 64-bit mode on these architectures is if you want more than 4GB of virtual address space in a process.
The ARM Cortex A15 supports 40-bit physical addresses, allowing up to 1TB of physical memory to be addressed. Probably not going to be enough for everyone forever, but definitely a lot more than you'll find in a typical server for the next couple of years. It only supports 32-bit virtual addresses, so you are limited to 4GB per process, but that's not a serious limitation for most people.
ARM already has 16 GPRs, so you can use them in pairs and have 8 registers for 64-bit operations. Not quite as many as x86-64, but four times as many as x86, so even that isn't much of an advantage. All of the other advantages that x86-64 has over x86, ARM has already.
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Yes, emulation is an option, but I don't think that ARM running x86 emulation layer will be competitive with native x86 CPUs. Didn't this happen to Itanium? Slow x86 performance and AMD's x86-64 resulted in virtually zero market for Itanium.
There are a lot of boxes out there doing nothing but serving files and printers, if ARM did start to be popular you can be sure that MS would be sure not to lose that business. And then, once you have the things installed, it suddenly makes sense to write some of your new programs to run on them...