Re: [Xen-devel] Cpupools and pdata_alloc

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 05/11/2010 07:25 PM, George Dunlap wrote:
> On Mon, May 10, 2010 at 11:48 PM, Juergen Gross
> <juergen.gross@xxxxxxxxxxxxxx>  wrote:
> > No. It happens when idle vcpus are allocated. At this time there is no
> > cpupool
> > existing, all physical cpus are marked as "free", e.g. they are in no pool
> > at
> > all.
> > Dom0 vcpus are allocated in Pool-0. This pool is created after allocation of
> > the idle vcpus.
> Yeah, I spent some time tracing through the init code yesterday and
> figured that out.  So it appears that at init time, regarding cpupools
> and schedulers:
> * init_idle_domain() calls schedule_init(), which calls ops->init()
> with a sort of "default" ops pointer.  It also calls sched_init_vcpu()
> for idle domain's vcpu 0, which will call ops->alloc_pdata for cpu 0.
> * smp_prepare_cpus will eventually call do_boot_cpu for each online
> cpu.  do_boot_cpu will initialize the idle_domain vcpu for that cpu,
> which will call ops->alloc_pdata for that cpu (again, with cpu 0
>   - At this point, all online cpus have had alloc_pdata called, albeit
> for the "default" ops structure in the scheduler
> * cpupool_create will create cpupool 0, calling sched_init(), which
> calls ops->init with the cpupool0 ops structure.
> * cpupool0_cpu_assign will then un-assign all online cpus from the
> "default" ops structure and re-assign them into cpupool 0.
> Re-assigning looks like this:
>   - First call alloc_pdata and then alloc_vdata for the new cpupool ops
> structure, for the physical cpu and idle vcpu respectively.
>   - Ticks will be disabled on the old ops structure, then resumed on
> the new ops structure
>   - The idle vcpu is added to the new pool
>   - Calls free_vdata and free_pdata on the old cpupool ops structure
> for the idle vcpu and physical cpu, respectively.
>
> Now all online cpus have idle vcpus and pdatas initialized, and set up
> for cpupool 0.
>
> Is that a pretty accurate picture?
Yes, this sounds correct.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
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