3 ms·
IO was only (barely) disk-bound when you gave a full core to the reader (i.e., you have to be careful not to use HW threads on the same core). This is not a pro
by mfp 18y ago
IO was only (barely) disk-bound when you gave a full core to the reader (i.e.,
you have to be careful not to use HW threads on the same core). This is not a
problem specific to OCaml --- I reproduced it with a standalone program
written in C that simply read the file: as soon as you have more stuff running
on the same core (in different hardware threads), the IO performance drops.
See
http://groups.google.com/group/wide-finder/browse_thread/thread/332f306893b37b0e?hl=en# http://groups.google.com/group/wide-finder/browse_thread/thr...
Also, and this came as quite a surprise, it turns out that mmap is slower than
read(2) on the T2K.
- iigs 18y agoWow, interesting. Thanks for the info and the link. This is a surprising and disappointing aspect of this CPU. Do you know if there's something about this (seemingly trivial) workload that is pathologically bad for this processor, or do you believe that the CPU is just wimpy? I've only ever had a glossy spec-sheet-level introduction to these at work. Given this load I don't see the value of "4 threads per core" that they proclaim on http://www.sun.com/processors/UltraSPARC-T1/specs.xml http://www.sun.com/processors/UltraSPARC-T1/specs.xml
- mfp 18y agoIt's just that the hardware threads are slow, I think --- compiling stuff on the T2K also took forever. It also seems to me that there's seemingly little value in having 4 threads per core: it forces you to parallelize programs that ran fine with normal cores just to match the performance you'd get without hardware threads...