[Xen-devel] "cpus" config parameter broken?

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

I've been looking into a report that vcpu pinning doesn't get preserved across a save/restore

(or migrate) and, debugging this, it's starting to look like the "cpus" config file parameter doesn't

work very well -- on 3.1 or unstable!  If anything is specified other than a single integer,

the code reverts to "any cpu".  I think I found this specific problem but there seems to be some

bad bit rot hiding behind that.   So before I go any further, I thought I'd ask a few questions:

 

1) Is the "cpus" parameter expected to work in a config file or is it somehow deprecated?

   (I see there is an "xm vcpu-pin" command so perhaps this is the accepted way to

   pin cpu's?)

2) Pinning via the "cpus" parameter calls vcpu_set_affinity() but I've always thought the term

    "affinity" expresses a preference not a restriction.  If the call to setaffinity did get

   made properly, would the scheduler really restrict the vcpu to certain pcpu's?  And

   what happens if the vcpu is ready to schedule but none of the restricted set of

   pcpu's is available?

3) Does "cpus" really have any real-world usage anyhow?  E.g. are most uses probably just

    user misunderstanding where "vcpu_avail" should be used instead?

 

Thanks,

Dan

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