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

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

I have blinders on since this discussion started with
my trying to figure out the syntax and semantics for
the "cpus" parameter as used in a config file, but:

> > - the v->cpu_affinity mask should never have bits set for
> 
> This is already the case.

No, with the cpus parameter, it is currently possible to
set bits in v->cpu_affinity mask for processors that don't
exist.

Perhaps this is the real bug then.  I will spin a patch
to implement the modulo behavior from "xm vcpu-set" for
the parsing of the cpus parameter and all will be well.

Thanks,
Dan

> -----Original Message-----
> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
> Sent: Thursday, January 10, 2008 1:50 PM
> To: dan.magenheimer@xxxxxxxxxx; Ian Pratt; 
> xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] "cpus" config parameter broken?
> 
> 
> 
> 
> 
> On 10/1/08 18:38, "Dan Magenheimer" 
> <dan.magenheimer@xxxxxxxxxx> wrote:
> 
> > As a logical consequence:
> >
> > - the v->cpu_affinity mask should never have bits set for
> >   processors that don't exist on the current physical system
> >   (although all bits set == "any" is probably an OK exception)
> 
> This is already the case.
> 
> > - the modulo behavior currently implemented in "xm vcpu-pin"
> >   and the config file "cpus" parameter should be removed, and
> 
> Possibly.
> 
> > - if cpu values are specified by "xm vcpu-pin" or "cpus"
> >   beyond the number of physical cpus, the xm command should
> >   fail.
> 
> Again, possibly. I don't see much wrong with a liberal 
> interpretation of
> otherwise incorrect cpu config parameters though. If we 
> tighten things up
> then we need to make it easier to access CPU topology info from within
> domain config files.
> 
>  -- Keir
> 
> > Agreed?
> >
> >> -----Original Message-----
> >> From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
> >> Sent: Wednesday, January 09, 2008 12:17 PM
> >> To: dan.magenheimer@xxxxxxxxxx; Ian Pratt;
> >> xen-devel@xxxxxxxxxxxxxxxxxxx
> >> Subject: Re: [Xen-devel] "cpus" config parameter broken?
> >>
> >>
> >> On 9/1/08 18:40, "Dan Magenheimer" 
> <dan.magenheimer@xxxxxxxxxx> wrote:
> >>
> >>> My opinion: CPU affinity/restriction should NOT be preserved
> >>> across migration.  Or if it is, it should only be preserved
> >>> when the source and target have the same number of pcpus
> >>> (thus allowing save/restore to work OK).  Or maybe it should
> >>> only be preserved for save/restore and not for migration.
> >>>>>>>>>>>> Comments? <<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> >>
> >> I agree with that. Unless save/restore is on the same machine
> >> (identified in
> >> some way) or at least has identical CPU topology as far as 
> we can see.
> >> Otherwise some higher-level entity needs to be smart enough
> >> to work out
> >> affinity during restore and issue the correct 'xm' commands
> >> (or equivalent).
> >>
> >>  -- Keir
> >>
> >>
> >>
> >
> 
> 
>


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