12806 Serial console polling burns CPU on VMware

Review Request #2568 — Created May 29, 2020 and updated

Information
gwr
illumos-gate
12806
Reviewers
general 
12806 Serial console polling burns CPU on VMware
Setup illumos guest under VMware with serial console

Notes here: https://github.com/jclulow/vmware-sercons

Booted with the change

press Esc to stop at loader prompt

observe laptop fan quiet


Boot the kernel with -kd

while stopped at kmdb prompt

observe laptop fan quiet


During later operation, break into kmdb (telnet send brk, or mdb -K)

observe laptop fan quiet


I did not observe any other behavior changes with this code.
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Description From Last Updated
gwr
tsoome
tsoome 
  1. Ship It!
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jlevon




   

   







  

 



 

  


   

   

    
 
jlevon


    
   


  

  

  



    




  1. 
 
    
  
    
   
    This clears the MSR delta bits. Did you confirm this doesn't break any expectations of the rest of the code? I think probably not due to no interrupts but...
    

    Looks like this is entirely VMWare-specific; neither qemu/kvm nor bhyve implement this.
    

    Why didn't you fix post-boot kmdb too (i.e. the asy via polledio interface)
    
  
    
 
    

 
    
  


    
 
    
 
      

  


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      re vmware: could you update the bug title to reflect what's getting fixed (vmware only)
      
 
      

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      OK.  Can you point me to the "post-boot kmdb" code I missed?
      
 
      

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      usr/src/uts/common/io/asy.c
      


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    typo: "pollng"
    
  
    
 
    

 
    
  


    
 
    
 
      

  

 
    


    

 
    

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      usr/src/uts/i86pc/boot/boot_console.c
      


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    typo: "pollng"
    
  
    
 
    

 
    
  


    
 
    
 
      

  

 
    


    

 
    

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    s/do to/to do/
    
  
    
 
    

 
    
  


    
 
    
 
      

  

 
    


    

 
    

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      usr/src/uts/common/io/asy.c
      


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    s/do to/to do/
    
  
    
 
    

 
    
  


    
 
    
 
      

  

 
    


    

 
    

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      usr/src/uts/i86pc/boot/boot_console.c
      


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    s/do to/to do/
    
  
    
 
    

 
    
  


    
 
    
 
      

  

 
    


    

 
    

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gwr




   

   

  

 



 















 



 

  

   




gwr




   

   

  

 



 















 





 

  

   




jlevon




   

   





  

 



 

  


   

   

    
 
jlevon


    
   


  

  

  



    




  1. 
 
    
  
    
   
    Since it seems your email address configured bounces:
    

    

    

    

    OK.  Can you point me to the "post-boot kmdb" code I missed?
    

    

    Looks like you found it. Presumably you've tested KMDB after boot as
    
well.
    

    I don't think you replied to my question about the MSR read
    
side-effects. I haven't really tried to untangle the handling of the
    
delta bits there, but presumably you have?
    
  
    
 
    

 
    
  


    
 
    
 
      

  


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      Yes, kmdb after boot worked the same.
      

      As for possible side effects: All these polling loops appear to run only where interrupts are disabled.
      
I did not observe any other side effects from the change.  I welcome suggestions for additional testing.
      
 
      

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gwr




   

   

  

 



 

  


   

   

    
 Review request changed

    
   


  

  

  











 



  

   
Testing Done:

   
    
     
Setup illumos guest under VMware with serial console
     Notes here: https://github.com/jclulow/vmware-sercons
     Booted with the change
     press Esc to stop at loader prompt
     observe laptop fan quiet
     

     
Boot the kernel with -kd
     while stopped at kmdb prompt
     observe laptop fan quiet
     

   + 
During later operation, break into kmdb (telnet send brk, or mdb -K)
   + observe laptop fan quiet
   + 

     
I did not observe any other behavior changes with this code.

   		
  



 










  

 









     

    

   

  

  

   
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