stockfish and number of cores

[lkaufman]

When I ran the new Stockfish 1.7 on an old quad, it reported the number of cores as 2, whereas older versions reported 4. So I did some checking, and I discovered that the older version is much faster with cores limited to 2 than with the setting at 4! So my questions are:
1. Is there something seriously wrong with this computer, based solely on this information? Any idea what the problem with it could be?
2. Is this behavior specific to Stockfish, or should I expect any MP chess program to run better with two cores set than with four, on this specific machine?

Thanks.

[mcostalba]

When I ran the new Stockfish 1.7 on an old quad, it reported the number of cores as 2, whereas older versions reported 4. So I did some checking, and I discovered that the older version is much faster with cores limited to 2 than with the setting at 4! So my questions are:
1. Is there something seriously wrong with this computer, based solely on this information? Any idea what the problem with it could be?
2. Is this behavior specific to Stockfish, or should I expect any MP chess program to run better with two cores set than with four, on this specific machine?

Thanks.

Probably you have HT enabled and so your old QUAD actually is a DUAL (sorry for revealing you this ).

SF, but also all the SMP engines, works best when the number of cores used matches the _real_ one, not the hyper threading inflated (doubled) one.

In your case I would say that the new HT detection code worked as expected (see my last post on Stockfish 1.7 thread).

[lkaufman]

No, it's definitely a quad (QX6700), but it seems to be acting strangely. Could it be that something was running in the background unknown to me that tied up one or two cores? I have rebooted so I can't check this, but I could redo the test to see if I still get a speedup by using only two cores.

[M ANSARI]

I can also confirm that there is a problem with CPU setting. It first defaulted to 4 cores on my Octa, then I forced 8 threads and noticed that on the F12 GUI it went back to 5 CPU's for some reason. I then removed the engine and re-installed it and made sure that 8 cores are running ... but it crashes horribly when I put it in a tourney. I re-tested the same hardware with R3 vs. ZM II and no crashes for 100 game tourney so I am pretty sure it is related to SF 1.7 and its 8 CPU implementation. Not sure what it is exactly, but maybe by forcing 8 threads some other parameter needs adjustment?

[M ANSARI]

Actually it seems that there is some incompatibility with F12 GUI with regards to the CPU's. It shows as 5 CPU's in the GUI but in task manager SF1.7 is clearly running all 8 cores. I have increased the split depth to 6 as recommend in the readme file and will try a tourney with these settings to see how it goes.

[zullil]

Actually it seems that there is some incompatibility with F12 GUI with regards to the CPU's. It shows as 5 CPU's in the GUI but in task manager SF1.7 is clearly running all 8 cores. I have increased the split depth to 6 as recommend in the readme file and will try a tourney with these settings to see how it goes.

If SF detects 8 cores, it will set the default value of minimum split depth to 7. Extensive testing indicated that this is an optimal value, though 6 is also quite good (and perhaps is even better than 7 on your hardware).

[Albert Silver]

Actually it seems that there is some incompatibility with F12 GUI with regards to the CPU's. It shows as 5 CPU's in the GUI but in task manager SF1.7 is clearly running all 8 cores. I have increased the split depth to 6 as recommend in the readme file and will try a tourney with these settings to see how it goes.

This isn't new. When I tested 1.6.3 in F12 and set it to SP, F12 still showed 2 CPUs yet the task manager confirmed SF was only using one.

[ernest]

I have increased the split depth to 6 as recommend in the readme file .

The same recommendation exists in the readme file since version 1.5