PowerEdge R7425: enabling Instruction Based Sampling

Question

Hi, I try to use Instruction Based Sampling (IBS) on a Dell PowerEdge R7425 machine equipped with 2 EPYC 7451 cpu running on Debian buster (Linux kernel 4.16.0.2, gcc 7.3.0), but Linux kernel does not detect that the CPU is capable of doing IBS. According to AMD developers, the BIOS needs to perform a series of things to enable IBS on this CPU model, and there may be an option in the BIOS to enable IBS. So, I updated the BIOS to the latest available version (version 1.3.6), and searched for such an option, but I couldn't find one.  Is there a BIOS option on R7425 for enabling IBS ? If not, could you add one ? According to the AMD developers, '[they] make IBS enable/disable available as part of [their] AGESA system that [they] release to BIOS vendors, so it should not be a particularly large amount of work ' Thanks. François

DELL-Josh Cr · Answer

Hi,

I do not see an option to enable or disable it. Can you try our live image and see if it is just an issue with Debian? https://www.dell.com/support/home/us/en/4/Drivers/DriversDetails?driverId=C31J4

JanJakub · Answer

Very timely topic! It seems that IBS is not enabled in other Dell's product lines - I don't see an option for enabling IBS in OptiPlex 5055 with Ryzen 2400G and bios 1.0.10 (april 2018) . The cpuid() instruction returns the information that IBS is disabled so I expect that testing it in Ubuntu/Debian or Dell live test system will return the same result.
Hopefully, this can be quickly resolved with a new bios with the option to enable it.

ftrahay · Answer

@JanJakub wrote:

Very timely topic! It seems that IBS is not enabled in other Dell's product lines - I don't see an option for enabling IBS in OptiPlex 5055 with Ryzen 2400G and bios 1.0.10 (april 2018) . The cpuid() instruction returns the information that IBS is disabled so I expect that testing it in Ubuntu/Debian or Dell live test system will return the same result.
Hopefully, this can be quickly resolved with a new bios with the option to enable it.

According to AMD developers (see this thread: https://community.amd.com/thread/230335), the problem affects all the Family 17h Model 1h CPUs (including Ryzen 2400G apparently).

For these cpus, the BIOS needs to "activate" IBS so that cpuid() state that IBS is enabled (and thus, Linux can load all the things related to IBS)

The code for enabling/disabling IBS is distributed by AMD to system vendors, so I hope Dell could quickly release a BIOS update that includes it.

ftrahay · Answer

Hi, I tried your live image, but IBS is still not detected by Linux, so this is not a Debian issue.

DELL-Josh Cr · Answer

Thanks, I will pass the request along.

ftrahay · Answer

I installed BIOS version 1.4.3 that, according to the changelog, includes "AGESA Naples PI-SP3_1.0.0.8 version", which I assume should contain the fix that enable IBS.

However, I could not find any option related to IBS in the BIOS, and Linux still doesn't detect that the CPU is IBS capable.

Did I miss an option in the BIOS ?

ftrahay · Answer

I upgraded the bios to version  1.5.6 (released on oct. 18th), but IBS is still disabled :(

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