[Qemu-devel] [RFC v1 PATCH 0/3] cpus: Convert cpu_index into a bitmap

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

This patch changes the way cpu_index is handed out to newly created
CPUs by tracking the allocted CPUs in a bitmap. More information and
the need for this patch is described in patch 2/3 of this series. These
generic changes are needed to support CPU hot plug/unplug on PowerPC.

cpu_index is allocated in cpu_exec_init() and freed (during CPU unplug) in
the newly added API cpu_exec_exit(). Currently all architectures call
cpu_exec_init() from instance_init and hence cpu_exec_exit() is called
from instance_finalize for all archs in this series.

Instead of adding instance_finalize to all archs, we could call
cpu_exec_exit() from the parent class (CPUClass.instance_finalize).
However archs like x86 and PowerPC want cpu_exec_init() to be moved to
realizefn from instance_init. Such movement will become easy with the
current approach. Eudardo's suggested alternative of making cpu_exec_exit()
idempotent

(http://lists.nongnu.org/archive/html/qemu-devel/2015-05/msg01241.html)

will also simplify this movement, but I think that would compilicate the
deallocation logic.

Another open question is about handling of holes correctly in the allocated
bitmap to support VM migration after CPU unplug. This was briefly discussed
here:

https://lists.gnu.org/archive/html/qemu-devel/2015-04/msg00560.html

Should cpu_exec_init() API support specifying of a particular cpu_index
in addition to returning the next available cpu_index by default ? I know
that QEMU cmdline semantics for CPU device add/delele haven't been defined
yet, but should we now make provision in cpu_exec_init() to allocate the
required cpu_index ?

Changes in v1
-------------
- Added Error argument to cpu_exec_init() so that it callers calling
  it from realizefn can collect errors.

v0: https://lists.gnu.org/archive/html/qemu-devel/2015-03/msg02950.html

Bharata B Rao (3):
  cpus: Add Error argument to cpu_exec_init()
  cpus: Convert cpu_index into a bitmap
  ppc: Move cpu_exec_init() call to realize function

 exec.c                      | 39 +++++++++++++++++++++++++++++++++++----
 include/exec/exec-all.h     |  2 +-
 include/qom/cpu.h           |  8 ++++++++
 target-alpha/cpu.c          |  8 +++++++-
 target-arm/cpu.c            |  3 ++-
 target-cris/cpu.c           |  8 +++++++-
 target-i386/cpu.c           |  8 +++++++-
 target-lm32/cpu.c           |  8 +++++++-
 target-m68k/cpu.c           |  8 +++++++-
 target-microblaze/cpu.c     |  8 +++++++-
 target-mips/cpu.c           |  8 +++++++-
 target-moxie/cpu.c          |  8 +++++++-
 target-openrisc/cpu.c       |  8 +++++++-
 target-ppc/translate_init.c | 15 +++++++++++++--
 target-s390x/cpu.c          |  3 ++-
 target-sh4/cpu.c            |  8 +++++++-
 target-sparc/cpu.c          |  3 ++-
 target-tricore/cpu.c        |  7 ++++++-
 target-unicore32/cpu.c      |  8 +++++++-
 target-xtensa/cpu.c         |  8 +++++++-
 20 files changed, 153 insertions(+), 23 deletions(-)

-- 
2.1.0