PC GAMESS/Firefly-related discussion club

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Sergey
qcplab@gmail.com

I would like to address an issue about efficiency of disk IO operations which is especially cruicial for the second MP2 integrals half-transformation as weel as other stages.

By its nature, this is mostly random reads/writes of intgrals between atom pairs, distributed over nodes. If 1-core - 1-disk hardware strategy is used, the target efficiency is function of disk access time  mostly. Hence, such the function as NCQ might be a good option to 'locally order' writes, lower the tears of HDD heads and increase efficiency.

However, if we consider modern MBs, they have typically SATA chips operating in 3 modes: SATA (Native IDE), AHCI and RAID. Note that NCQ is a part of the 2nd and the 3rd mode, but I didn't found reliable info about the first mode.

If OS is WindowsXP, then SATA (Native IDE) mode may NOT use NCQ, as this support is implemented officially only in OS LH (Vista) or W7. More to that, enabling ACHI on some controllers results in degrading performance by 10% or so as the driver actually maps ACHI to SATA and that's all it does.

For the LH/W7, there is such the support for NCQ and other functions of ACHI natively, so they promise ~ 5% average performance boost, but on case for random writes as we have in MP2 second half-transformation, that might be much more pronounced.

The question to the authors of Firefly then arises about NCQ, drivers and PCGAMESS, did they perform such the tests with NCQ enabled/disabled for WinXP/LH/7 for the MP2 and if yes, what were the results? Or maybe, suggestions what the results might be?

Otherwise it would be a good idea to perform such the tests. I will report here if I found something interesting on topic.

Thank you!