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Gwinel / likwid

Automatically exported from code.google.com/p/likwid
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Disabling prefetching on Intel Sandybridge doesn't work #157

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
 ./likwid-features  -c 1 -u DCU_PREFETCHER
-------------------------------------------------------------
CPU name:   Intel Core SandyBridge processor 
CPU core id:    1 
-------------------------------------------------------------
Fast-Strings:           enabled
Automatic Thermal Control:  enabled
Performance monitoring:     enabled
Branch Trace Storage:       supported
PEBS:               supported
Intel Enhanced SpeedStep:   enabled
MONITOR/MWAIT:          supported
Limit CPUID Maxval:         disabled
XD Bit Disable:         enabled
IP Prefetcher:          enabled
Hardware Prefetcher:        enabled
Adjacent Cache Line Prefetch:   enabled
DCU Prefetcher:         enabled
-------------------------------------------------------------
*************************************************************
DCU_PREFETCHER: disabled

Failed to write data through daemon: daemon returned error 4 'failed to 
read/write register' for cpu 1 reg 0x1a0

----

Though it says "disabled", the write to msr actually failed.

Any ideas how to fix this?

Original issue reported on code.google.com by devesh.d...@gmail.com on 3 Jun 2014 at 7:25

GoogleCodeExporter commented 9 years ago 
I will check on this but for your information: the SandyBridge architecture 
does not provide the (de)activation of the prefetchers. All prefetcher bits are 
"reserved" by Intel. I think the likwid-features code does not exclude 
architectures that do not have these bit anymore.

Original comment by Thomas.R...@googlemail.com on 5 Jun 2014 at 8:26

GoogleCodeExporter commented 9 years ago 
Hi,
the bits are only available at biosbits.org . But as far as I understood the 
BIOS can still disable their usage. In short: I implemented it but also on my 
machine it did not work. Same error. It may be I made a mistake. Intel says it 
is not a good idea to toggle prefetchers in normal running state.

Jan

Original comment by jan.trei...@gmail.com on 5 Jun 2014 at 8:39

GoogleCodeExporter commented 9 years ago 
I added a model check to cpuFeatures.c (v3.1 branch), the file that contains 
the setter and unsetter for the feature flags. 

Mark issue as fixed.

Original comment by Thomas.R...@googlemail.com on 29 Jul 2014 at 11:07