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Re: [Libvir] Start NUMA work



On Tue, Sep 11, 2007 at 04:28:00PM +0100, Richard W.M. Jones wrote:
> Daniel Veillard wrote:
> >  Okay enclosed is a first patch to add the new entry point for getting
> >the available memeory in the NUMA cells:
> >
> >/**
> > * virNodeGetCellFreeMemory:
> > * @conn: pointer to the hypervisor connection
> > * @freeMems: pointer to the array of unsigned long
> > * @nbCells: number of entries available in freeMems
> > *
> > * This call allows to ask the amount of free memory in each NUMA cell.
> > * The @freeMems array must be allocated by the caller and will be filled
> > * with the amounts of free memory in kilobytes for each cell starting
> > * from cell #0 and up to @nbCells -1 or the number of cell in the Node
> > * (which can be found using virNodeGetInfo() see the nodes entry in the
> > * structure).
> > *
> > * Returns the number of entries filled in freeMems, or -1 in case of 
> > error.
> > */
> >
> >int 
> >virNodeGetCellsFreeMemory(virConnectPtr conn, unsigned long *freeMems,
> >                          int nbCells)
> 
> So you're using "unsigned long" here to mean 32 bits on 32 bit archs, 
> and 64 bits on 64 bit archs?
> 
> A purely 32 bit freeMem will allow up to 4095 GB of RAM per cell.  But 
> in reality up to 2047 GB of RAM because mappings in other languages will 
> probably be signed.
> 
> High-end users are already decking out PCs with 128 GB of RAM.  If they 
> double the RAM every year, we'll hit this limit in 4 years[1].  So is it 
> worth using an explicit 64 bit quantity here, or using another base (MB 
> instead of KB for example)?  Or do we just think that all such vast 
> machines will be 64 bit?

  Well we already use unsigned long in KB for memory quantities in
libvirt, I just reused that, I doubt we will see more than 64GB for
32bits CPU ever, that's already stretching the limits

> >  based on the feedback, it seems it's better to provide an API checking
> >a range of cells. This version suggest to always start at cell 0, it could 
> >be
> >extended to start at a base cell number, not a big change, is it needed ?
> 
> On the one hand, subranges of cells could be useful for simple 
> hierarchical archs.  On the other hand (hypercubes) useful subranges 
> aren't likely to be contiguous anyway!

  for anything non-flat it's hard to guess and for anything flat placement
means basically checking all cells to find the optimum

> >The patch adds it to the driver interfaces and put the entry point
> >needed in the xen_internal.c module xenHypervisorNodeGetCellsFreeMemory() .
> 
> As for the actual patch, I'm guessing nothing will be committed until we 
> have a working prototype?  Apart from lack of remote support it looks fine.

  yes, and right remote is something I didn't tried to look at yet, I hope
returning arrays of values won't be a problem.

> >  Now for extending virConnectGetCapabilities() it is a bit messy not not
> >that much. First it's implemented on Xen using 
> >xenHypervisorGetCapabilities,
> >unfortunately it seems the easiest way to get the NUMA capabilities is by
> >asking though xend. Calling xend_internals.c from xen_internals.c is not
> >nice, but xenHypervisorGetCapabilities() is actually noty using any
> >hypervisor call as far as I can see, it's all about opening/parsing
> >files from /proc and /sys and returning the result as XML, so this could
> >as well be done in the xend_internals (or xen_unified.c) module.
> 
> Yeah, best just to move that common code up to xen_unified.c probably. 

  yes my though, except for the global variable used.

> In any case the Xen "driver" is so intertwined that it's really just one 
> big lump so calling between the sub-drivers is unlikely to be a problem.

  heh :-\

Daniel

-- 
Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/


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