I was talking here recently of the possibility of a Dreadnought
64-bit only language for the RPi, but it seems that I might have been pipped at the post by the DEC Alpha.As far as I can gather, the Alpha instruction set only supported 64 and 32 bit variables.
Am I misinformed?
If I'm reading this:
I designed and programmed a system that ran on Alphaservers in 1999-2001 but IIRC these were EV4 or EV5 chips, running DEC's Mach-based Unix and were programming in C. I was certainly using char and char[] array variables but never needed to peer into C's guts to see what it was up to at the memory addressing level or how it messed with chars in those 32 bit registers.
I only found two performance crimes in the innards of the Alpha chip or DEC Unix:
(1) the Mach kernel could multi-task different low-level API-modules but insisted on single-threading queues for each different API-module, which could and did give horrid performance (think of a data warehouse with with a segmented fact table - any time you applied, say chmod() or a resizing operation to it this affected all its segments and so the operation was horribly slow because the Mach kernel serialised the operation as applied to each individual segment.
(2) we did a lot of stuff using very large in-memory B-trees, but it turned out that each node needed 3 mallocs (pointers, key and data all had separate, linked chunks of memory) so operations such as building a large tree were also very slow because (surpise!) malloc was serialised too). The development server (with an EV4 chip) could never add nodes at better than 700/sec using library code. We discovered that malloc() speed was the problem, rewrote the B-tree code (thanks Sedgewick!) to use one malloc per node and got a 3x speedup to 2100/sec Not enough. We needed at least 7500/sec, so I wrote a new memory scheme in which malloc() grabbed RAM in megabyte multiples and stacked the B-tree nodes in these chunks, grabbing another as the current one got filled. This got the speed up to
25,000/sec so this particular issue was never a problem after that.Apart from these two points, the Alpha servers were great: even the EV4 box could support 10 developers, each with two logins and their own datawarehouse instance. At the time this was something I didn't expect to see, considerng that server was small enough to live under one of our desks.
-- Martin | martin at Gregorie | gregorie dot org
EV4 and EV5 Alphas only supported 64 and 32 bit instructions.
EV6 and EV7 Alphas did support 8 and 16 bit instructions.
The size of /instructions/ on the alpha was always 32 bits, the question is the size of the data which integer arithmetic instructions handled.
All variants of the alpha only worked with 32 bit or 64 bit registers, later version having some additional byte/word extension op codes. This is broadly similar to ARMv8 which works on 32 bit or 64 bit registers and has additional instructions for manipulating 8 bit and 16 bit data.
---druck
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