On Wed, Mar 18, 2015 at 12:04:04PM +0530, Bharata B Rao wrote: > On Wed, Mar 18, 2015 at 11:49:59AM +1100, David Gibson wrote: > > On Fri, Mar 13, 2015 at 05:26:36PM +0530, Bharata B Rao wrote: > > > From: Bharata B Rao <bharata....@gmail.com> > > > > > > Currently CPUState.cpu_index is monotonically increasing and a newly > > > created CPU always gets the next higher index. The next available > > > index is calculated by counting the existing number of CPUs. This is > > > fine as long as we only add CPUs, but there are architectures which > > > are starting to support CPU removal too. For an architecture like PowerPC > > > which derives its CPU identifier (device tree ID) from cpu_index, the > > > existing logic of generating cpu_index values causes problems. > > > > > > With the currently proposed method of handling vCPU removal by parking > > > the vCPU fd in QEMU > > > (Ref: http://lists.gnu.org/archive/html/qemu-devel/2015-02/msg02604.html), > > > generating cpu_index this way will not work for PowerPC. > > > > > > This patch changes the way cpu_index is handed out by maintaining > > > a bit map of the CPUs that tracks both addition and removal of CPUs. > > > > > > I am not sure if this is the right and an acceptable approach. The > > > alternative is to do something similar for PowerPC alone and not > > > depend on cpu_index. > > > > > > I have tested this with out-of-the-tree patches for CPU hot plug and > > > removal on x86 and sPAPR PowerPC. > > > > How does this interact with the tweaking of cpu indexes that spapr > > does in order to configure the guest SMT mode on POWER7 and POWER8 > > systems? > > I am not changing the mapping of cpu_index to cpu_dt_id. So nothing > should be change. Can you please point me to the piece of tweaking code > that you are referring to above ?
Ah, I thought it actually adjusted the cpu_index values, rather than
mapping them to different cpu_dt_id values. Maybe it used to, or
maybe I just misremembered.
Never mind, should be fine.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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