[SERVER-82030] "Illegal instruction" on EL7 Ivy Bridge CPU Created: 10/Oct/23  Updated: 16/Oct/23  Resolved: 16/Oct/23

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: 5.0.21
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Thomas Fromm Assignee: Noopur Gupta
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Attachments: Text File cpuinfo.txt     Text File gdb.txt    
Issue Links:
Related
is related to MONGOSH-1604 "Illegal instruction" on mongosh 2.0.... Closed
Operating System: ALL
Steps To Reproduce:

"Illegal instruction" happens, when executing mongod on CentOS 7 on a system with Ivy Bridge CPU.

Participants:

 Description   

The issue seems similar to: https://jira.mongodb.org/browse/MONGOSH-1604

Attached is cpuinfo and gdb output of: gdb -ex run -ex bt -ex 'disassemble $rip-100,$rip+100' --batch --args mongod

Since we're running a lot of microservers with this generation of CPUs, the support of it is important to us.

 

 



 Comments   
Comment by Noopur Gupta [ 12/Oct/23 ]

Hi tf@doc-cirrus.com

AVX instructions(Single Instruction/Multiple dataset SIMD) are set of instructions added in the processors which contributes to improving performance.

AVX (Advanced Vector Extension) requirement was added on MongoDB v5+ since it improves overall mongod performance capabilites.. Since most of the latest CPUs support AVX, MongoDB decided to provide one single support build type with AVX instructions.

You can also find this helpful post on the Developer forum https://www.mongodb.com/community/forums/t/one-more-time-about-mongo-5-cpu-requirements/168858.

Let us know if you have further questions on this.

Thanks
Noopur

Comment by Thomas Fromm [ 11/Oct/23 ]

I thought the lack of avx was only true for the previous microserver generation shipped with G5420, but the problem affects also the current series of HPE Microserve Gen10+ V2 shipped with Pentium G6405.

So my questions at this point: Which benefits does mongod have from relying on avx that strong?

Comment by Thomas Fromm [ 10/Oct/23 ]

I noticed a bit late the requirement of AVX inside the documentation: https://www.mongodb.com/docs/v5.0/administration/production-notes/

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