7 Replies Latest reply on Oct 5, 2015 2:07 PM by sridutt

    DVFS on Intel SandyBridge

    sridutt

      Hi All,

      I wanted to experiment with DVFS on Intel SandyBridge and through the Intel Manual 3B, I see that the DVFS is achieved on SandyBridge using Enhanced Intel SpeedStep.

      It says that IA32_PERF_CTL could be set to achieve DVFS. However the Manual does not explain how to set the lower 16 bits in IA32_PERF_CTL to achieve this. I went across searching on different forums to ascertain how to set this to no avail. However, what I could learn is that the 16 bits are divided into two 8-bit blocks that specify the Multiplier and VID.

      I also found that the multiplier can be found on intel sandy bridge as

      • [CPU frequency] = BCLK x [CPU multiplier].

       

      I am using a Xeon E5-2680 with 2.7GHz. The data sheet says the BCLK0 and BCLK1 are 100MHz(Table:6-11). So the current multiplier seems to be 27. The VID range is 0.60V-1.35V.

      1. Now if I have to scale the frequency, do the go about changing 8-MSB(15-8) to any value lesser than 27 only?

      2. Or do I need to change the 8-LSB(7-0) between 0.6 and 1.35V.

      I am aware that SandyBridge has a limited set of P-states from P0 to PN and I just can't go about setting the 16-bits as per my will.

      So, What I basically wanna know is how do I do DVFS on SandyBridge?

      PS: Please correct me if my understanding so far is incorrect.

       

      Thanks in advance.

      Best,

      Sridutt