Re: [XenPPC] [PATCH] Enable SMP and IPIs

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Oct 24, 2006, at 9:29 AM, Michal Ostrowski wrote:

> On Tue, 2006-10-24 at 00:22 -0400, Amos Waterland wrote:
> > This patch enables SMP and IPIs.  It works reliably on JS20 and JS21
> > blades.  It is not quite ready for submission, but I would greatly
> > appreciate any comments.
> >
> > Note that the flurry of IPIs generated by domain creation seems to  
> > be a
> > waste of time.  Xen on x86 doesn't actually to do anything in  
> > response
> > to them, so I have made Xen on PPC properly deliver the event  
> > check but
> > then do nothing as well.  Comments?
> >
> > The important thing this patch is missing is the ability to invoke
> > functions on a remote CPU, and I have left it out because I am not  
> > yet
> > happy with the convention, which is to grab a lock, put the target
> > address in a single global shared variable, invoke a memory  
> > barrier, and
> > send the IPI.  I am hoping to avoid a lock around that operation by
> > making a per-IPI-destination-CPU structure with lock, address, and  
> > ack
> > fields.  Comments?
> The strategy I decided upon to use in rhype was to maintain an  
> array of
> function "records" (fn ptr + arg data), and a bit-map per-cpu
> identifying which ones were active.  If I want to run something on
> another CPU, I find and fill in and empty function record for the  
> target
> CPU and then set the bit in the bitmap.  The receiver CPU checks to  
> see
> if there is work to be done and if so, runs the specified function.
> This mechanism makes the caller responsible for providing for managing
> return values/ACKs.
>
> I hope to use this to drive RCU activity as well, so it is not tied  
> down
> to an actual IPI vector occurring.  In fact, I have not yet has a need
> to actually depend on an IPI from the mpic.
Ahh yes.. the hi frequency periodic timer on a hypervisor that does  
not interrupts. :-P
How would you take an IPI anyway?!
I guess you would use it to interrupt an LPAR?

-JX



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