topic Sometimes access to some MSR in Software Tuning, Performance Optimization & Platform Monitoring

Disabling Hardware Prefetch and Adjacent Cache Line Fetch in Sandy/Ivy Bridge without BIOS Support

Adam_J_3 — Wed, 31 Jul 2013 21:31:06 GMT

Hi, I have 2 computers with sandy bridge-e and ivy bridge processors respectively and neither one them have BIOS options for disabling hardware prefetch and the adjacent cache line fetch options.

Is there any way (i.e. a MSR, etc) to disable these options in the processor?

Thanks!

Adam

Sometimes access to some MSR

Bernard — Thu, 01 Aug 2013 17:16:19 GMT

Sometimes access to some MSR registers is locked even from kernel mode.If I am not wrong some functionality can be accessed by switching to SMM mode.

Hello Adam,

Patrick_F_Intel1 — Thu, 01 Aug 2013 18:51:23 GMT

Hello Adam,

Currently there is no publicly available method to enable/disable the hardware prefetchers using MSRs.

I'm checking whether the folks who control this info will reconsider that policy now that (at least some) BIOSes aren't providing an enable/disable prefetcher option.

I don't know when I will get a reply back.

In order to build the case for disclosing the settings, can you describe the reasons why you'd like to enable/disable the prefetchers?

Pat

Hi Pat,

Bernard — Fri, 02 Aug 2013 15:34:41 GMT

Hi Pat,

does it mean that such a access (through MSR) is possible, but is only aavailable for Bios vendors?

I'm a graduate student

Adam_J_3 — Fri, 02 Aug 2013 22:08:22 GMT

I'm a graduate student researcher using your processors as a test bed for a paper we're trying to get published. I need the system to be as quiet as possible and I believe that the prefetcher might be introducing variability in our results.

I ended up buying another motherboard that supports disabling the prefetchers, but I'd still prefer to do it from linux (and to be able to test if the prefetcher is enabled easily from linux).

>>>I ended up buying another

Bernard — Tue, 06 Aug 2013 09:31:17 GMT

>>>I ended up buying another motherboard that supports disabling the prefetchers, but I'd still prefer to do it from linux (and to be able to test if the prefetcher is enabled easily from linux).>>>

I do not think if you can do it from kernel mode.Some of the low level functionality of CPU is accessed through the Bios which may switch to SMM mode of operation.