--- Sorry, I was borderline insulting. I'm getting pressure on personal fronts other than just here. But my degree is in computer science and I've had almost 20 years experience programming things as small as 8080's w/ 4K ram on up. I'm familiar with 'cost' of emulation.
> Let's try to keep the discussion civilized, shall we?--- Certainly. > > Compile option or not, 64-bit arithmetic is unacceptable on IA32. The > introduction of LFS was bad enough, we don't need yet another proof that > IA32 sucks. Especially when there *are* better alternatives. === So if it is a compile option -- the majority of people wouldn't be affected, is that in agreement? Since the default would be to use the same arithmetic as we use now.
In fact, I posit that if anything, the majority of the people might be helped as the block_nr becomes a a 'typed' value -- and perhaps the sector_nr as well. They remain the same size, but as a typed value the kernel gains increased integrity from the increased type checking. At worst, it finds no new bugs and there is no impact in speed. Are we in agreement so far?
Now lets look at the sites want to process terabytes of data -- perhaps files systems up into the Pentabyte range. Often I can see these being large multi-node (think 16-1024 clusters as are in use today for large super-clusters). If I was to characterize the performance of them, I'd likely see the CPU pegged at 100% with 99% usage in user space. Let's assume that increasing the block size decreases disk accesses by as much as 10% (you'll have to admit -- using a 64bit quantity vs. 32bit quantity isn't going to even come close to increasing disk access times by 1 millisecond, really, so it really is going to be a much smaller fraction when compared to the actual disk latency).
Ok...but for the sake of argument using 10% -- that's still only 10% of 1% spent in the system. or a slowdown of .1%. Now that's using a really liberal figure of 10%. If you look at the actual speed of 64 bit arithmatic vs. 32, we're likely talking -- upper bound, 10x the clocks for disk block arithmetic. Disk block arithmetic is a small fraction of time spent in the kernel. We have to be looking at *maximum* slowdowns in the range of a few hundred maybe a few thousand extra clocks. A 1000 extra clocks on a 1G machine is 1 microsecond, or approx 1/5000th your average seek latency on a *fast* hard disk. So instead of 10% slowdown we are talking slowdowns in the 1/1000 range or less. Now that's a slowdown in the 1% that was being spent in the kernel, so now we've slowdown the total program speed by .001% at the increase benefit (to that site) of being able to process those mega-gig's (Pentabytes) of information. For a hit that is not noticable to human perception, they go from not being able to use super-clusters of IA32 machines (for which HW and SW is cheap), to being able to use it. That's quite a cost savings for them.
Is there some logical flaw in the above reasoning?
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