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E5-1650 v4 Throttling
#1
Hi;

   I built a new system with a Xeon E5-1650 v4, and I've noticed that several stress programs, like Prime-95, cause the system to throttle to a speed below the base frequency (3500 MHz which is below the base 3600 MHz). This is even though the temp.s seem o.k., and happens if I run even just one Prime-95 thread (for the core running that thread).

Some stress test program run (all 6 cores) at 3800 MHz without an apparent issue, like the Intel Processor Diagnostic tool 'CPU load' test. But the same programs FPU test shows all cores running at only 35X.

  Sadly, I've come to suspect that this is just something this Xeon does (by design), but I was hoping to use HWINFO to verify if that was the case. Would you expect the HWINFO "performance limit reasons' to display if this is an expected built-in throttling (verses some type of issue)?

When I see throttling, I see that the 'IA: Turbo attenuation (MCT)' is listed as 'yes', but this seems to be on sometimes when I'm not even running an stressful programs.

Also, it seems that the HWINFO 'CPU Package' power display seems to be very low. Is this supposed to be the total CPU power or something else?

The screen captures below are with a 'Balanced' power profile, running one thread of Prime-95 (with AVX/AVX2 enabled) showing 3500 MHz on the Prime-95 core. If I use the 'Performance' profile, then the other cores not running Prime-95 show 3800 MHz.

I can run 12 threads of Prime-95 at 3800 MHz if I disable 'AVX/AVX2' in the Prime-95 settings file. As far as I can tell, this isn't a total package power issue as I can run all 6 cores without throttling (for some stress tests like Prime-95 w/o AVX enabled), while throttling seems to happen with just one core 100% busy for Prime-95 w/AVX (for those cores running Prime-95 at the time).


Thanks;

P.S.- This is under Windows 7 64-bit, running HWINFO 5.44 on an ASUS X99-E WS/USB 3.1 motherboard.


   
   
   
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#2
There can be several reasons for clock throttling, but your case is easy to explain Smile
Since AVX workloads are usually more power demanding that other instruction sets, later Intel CPUs (including yours) automatically limit operating frequency when AVX code is executed. This happens no matter what the actual power consumption is, to prevent a potential excursions. Your CPU specification is:
AVX Max Turbo Frequency (GHz): 3.5

Indeed the CPU Package Power value seems not to be valid. This happens usually if SVID support is disabled in BIOS. In this case CPU internal power reporting doesn't work.
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