[Qemu-devel] [PATCH v3 0/7] Runtime pagesize computation

[Peter Maydell]

(I posted version 2 way back in June...)

The basic idea here is that:
 * the target CPU implementation has to opt into variable page size
   by defining TARGET_PAGE_BITS_VARY, and then calling
   set_preferred_target_page_bits() in its realize function
   with whatever the CPU as instantiated actually requires
 * the machine also has to opt in, by specifying a new MachineClass
   field which states the value they guarantee will be no greater
   than the preferred page size for any CPU they create
 * we finalize the decision about page size in cpu_exec_init_all()
   (and then later attempts to create CPUs which can't cope with
   that decision are failed)

I would ideally have liked to finalize things much later, but
this is in practice hugely difficult because so many things
(in particular all the address space/memory system code)
assume the target page size is known.

Note that setting minimum_page-bits for a machine is a migration
compatibility break (the RAM migration format assumes both sides
have the same idea of a page size). In v3 I have included a
patch which adds the target-page-bits to the migration stream
so that you get a reasonably nice error message if you try
to migrate between source and destination which disagree about
the page size.

This could in theory be extended to the user-mode binaries,
but for the moment I have just required them to define a
fixed TARGET_PAGE_BITS.


Patches 1-3 have been reviewed, so 4-7 are the interesting
ones.

REQUEST FOR TESTING/PERFORMANCE BENCHMARKING:

I have only very lightly tested these and haven't attempted
to measure performance at all. Further testing and
benchmarking reports are therefore welcome.

In particular I would like to know how much of an
effect on TCG performance the assert() in the definition
of TARGET_PAGE_BITS has, so comparisons of all three configs:
 * before this patchset (ie TARGET_PAGE_BITS compile time const)
 * with this patchset (with assert in TARGET_PAGE_BITS)
 * this patchset, but with the assert commented out


Changes v2->v3:
 * rebased
 * added new patch to migrate the page size if it's not the default
 * virt-2.7 and earlier machines stick with the old
   default page size to avoid a compat break
 * in patch 3, v_l1_size is pulled into a local when we're
   using it as a loop upper bound

thanks
-- PMM


Peter Maydell (4):
  cpu: Support a target CPU having a variable page size
  migration/savevm.c: migrate non-default page size
  target-arm: Make page size a runtime setting
  hw/arm/virt: Set minimum_page_bits to 12

Vijaya Kumar K (3):
  migration: Remove static allocation of xzblre cache buffer
  exec.c: Remove static allocation of sub_section of sub_page
  translate-all.c: Compute L1 page table properties at runtime

 exec.c                 | 47 ++++++++++++++++++++++++++++++---
 hw/arm/virt.c          |  4 +++
 include/exec/cpu-all.h |  9 +++++++
 include/hw/boards.h    |  7 +++++
 include/qemu-common.h  | 12 +++++++++
 migration/ram.c        |  4 ++-
 migration/savevm.c     | 49 ++++++++++++++++++++++++++++++++++
 target-arm/cpu.c       | 24 +++++++++++++++++
 target-arm/cpu.h       |  9 ++++---
 translate-all.c        | 71 ++++++++++++++++++++++++++++++++------------------
 vl.c                   | 10 +++++++
 11 files changed, 213 insertions(+), 33 deletions(-)

-- 
2.7.4