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Published 20 hours ago • verified publisher icon intel

65% - 94% mba cos value generates the same result 90%

Open congxu2016 opened this issue 7 years ago • 6 comments

I am using pqos library (i.e. pqos_mba_set()) to set the MBA COS dynamically. I found no matter what value I use between 65% - 94% on my machine, the MBA COS is ultimately set to 90%. My skylake platform is Xeon Gold 6150. OS is ubuntu 16.04.2 (kernel 4.13).

congxu2016 avatar Apr 05 '18 22:04 congxu2016

Thanks for contacting us with this issue. We will investigate and report back when we have updates.

Regards, Marcel

mdcornu avatar Apr 09 '18 09:04 mdcornu

I also noticed this, I tried writing the MSR directly using wrmsr and noticed it still returned "0xA" which corresponds to 100 - 0xA or 90% of available bandwidth.

MBA MSR starts at address 0xD50

To set COS1, that would be address 0xD50+1 => 0xD51.

In my case, I tried to set it to 70% available bandwidth, that's translates to 30% throttle or 0x1E.

# rdmsr 0xD51
0

# wrmsr 0xD51 0x1E

# rdmsr 0xD51
a    <== Should be 0x1e not 0xa

meteorfox avatar Jun 02 '18 01:06 meteorfox

Hi,

Has this issue been resolved, I'm also getting a similar behavior on Intel(R) Xeon(R) Silver 4114 i.e., the MBA levels of 70% & 80% are ultimately set to 90%

gureya avatar Nov 04 '19 12:11 gureya

Similar behavior is observed on Intel(R) Xeon(R) Gold 6126 CPU. Not only for MBA levels, for some values of LLC cache ways values are not set properly. For example, When I try to set LLC cache ways to 0x400, it is updating to 0x600.

madhura-a avatar Mar 02 '20 05:03 madhura-a

These issues are under investigation, thanks for your patience.

limitedge avatar Mar 10 '20 19:03 limitedge

This is a known issue on certain generations of Xeon eg Skylake and Cascadelake which should now be in the sightings report, and this will be fixed in subsequent generations. Thanks

limitedge avatar Mar 17 '20 18:03 limitedge