Disabling hardware prefetchers on KNL

[Shilpa_B_]

Hi,

I am working on understanding the effect of prefetchers on user programs. On SandyBridge I could turn on/off prefetching by setting/resetting bits of MSR 0x1a4. However I could not find any documentation regarding the same for Knights Landing (KNL) architecture. So, I would like to know if is there a way by which hardware prefetching on KNL can be selectively turned on/off. 

Thanks,

Shilpa

[Sebastian_S_Intel]

Hi Shilpa,

have you tried the way that worked for you on SandyBridge platform?
The same MSRs should work as it is a common part of the cpu.
0x1a4 MSR controls L1/L2 HWPs:
- 0x0 both enabled
- 0x3 both disabled

Hope it helps,
Sebastian

[Shilpa_B_]

Hi Sebastian,

Thanks for the quick reply. I tried the same way as I was doing for SandyBridge and it worked. However, unlike SandyBridge where 4-bits are reserved for four prefetchers ( two for L1 and L2 each), on KNL only two bits are reserved for prefetchers one for L1 and L2 each.

Thanks,

Shilpa 

[Sebastian_S_Intel]

I'm glad that it works for you Shilpa,

​You are also right about the difference between Phi and regular Xeons.
Just in case you missed it here is more detailed explanation of HWP MSRs for regular Xeons: https://software.intel.com/en-us/articles/disclosure-of-hw-prefetcher-control-on-some-intel-processors 

Regards,
​Sebastian