[Qemu-devel] [RFC 00/28] bitmap handling optimization

[Juan Quintela <quintela@redhat.com>]

Hi

This series split the dirty bitmap (8 bits per page, only three used)
into 3 individual bitmaps.  Once the conversion is done, operations
are handled by bitmap operations, not bit by bit.

- *_DIRTY_FLAG flags are gone, now we use memory.h DIRTY_MEMORY_*
   everywhere.

- We set/reset each flag individually
  (set_dirty_flags(0xff&~CODE_DIRTY_FLAG)) are gone.

- Rename several functions to clarify/make consistent things.

- I know it dont't pass checkpatch for long lines, propper submission
  should pass it. We have to have long lines, short variable names, or
  ugly line splitting :p

- DIRTY_MEMORY_NUM: how can one include exec/memory.h into cpu-all.h?
  #include it don't work, as a workaround, I have copied its value, but
  any better idea?  I can always create "exec/migration-flags.h", though.

- The meat of the code is patch 19.  Rest of patches are quite easy
(even that one is not too complex).

Only optimizations done so far are
set_dirty_range()/clear_dirty_range() that now operates with
bitmap_set/clear.

Note for Xen: cpu_physical_memory_set_dirty_range() was wrong for xen,
see comment on patch.

It passes virt-test migration tests, so it should be perfect.

I post it to ask for comments.

ToDo list:

- create a lock for the bitmaps and fold migration bitmap into this
  one.  This would avoid a copy and make things easier?

- As this code uses/abuses bitmaps, we need to change the type of the
  index from int to long.  With an int index, we can only access a
  maximum of 8TB guest (yes, this is not urgent, we have a couple of
  years to do it).

- merging KVM <-> QEMU bitmap as a bitmap and not bit-by-bit.

- spliting the KVM bitmap synchronization into chunks, i.e. not
  synchronize all memory, just enough to continue with migration.

Any further ideas/needs?

Thanks, Juan.

PD.  Why it took so long?

     Because I was trying to integrate the bitmap on the MemoryRegion
     abstraction.  Would have make the code cleaner, but hit dead-end
     after dead-end.  As practical terms, TCG don't know about
     MemoryRegions, it has been ported to run on top of them, but
     don't use them effectively.

The following changes since commit a684f3cf9b9b9c3cb82be87aafc463de8974610c:

  Merge remote-tracking branch 'kraxel/seabios-1.7.3.2' into staging (2013-09-30 17:15:27 -0500)

are available in the git repository at:


  git://github.com/juanquintela/qemu.git bitmap.next

for you to fetch changes up to a90a941c24589d618b3d8461675d9b5afb3288cb:

  memory: cpu_physical_memory_clear_dirty_range() now uses bitmap operations (2013-10-09 12:30:35 +0200)

----------------------------------------------------------------
Juan Quintela (28):
      Move prototypes to memory.h
      memory: cpu_physical_memory_set_dirty_flags() result is never used
      memory: cpu_physical_memory_set_dirty_range() return void
      exec: use accessor function to know if memory is dirty
      memory: create function to set a single dirty bit
      exec: create function to get a single dirty bit
      memory: make cpu_physical_memory_is_dirty return bool
      exec: simplify notdirty_mem_write()
      memory: all users of cpu_physical_memory_get_dirty used only one flag
      memory: set single dirty flags when possible
      memory: cpu_physical_memory_set_dirty_range() allways dirty all flags
      memory: cpu_physical_memory_mask_dirty_range() allways clear a single flag
      memory: use DIRTY_MEMORY_* instead of *_DIRTY_FLAG
      memory: use bit 2 for migration
      memory: make sure that client is always inside range
      memory: only resize dirty bitmap when memory size increases
      memory: cpu_physical_memory_clear_dirty_flag() result is never used
      bitmap: Add bitmap_zero_extend operation
      memory: split dirty bitmap into three
      memory: unfold cpu_physical_memory_clear_dirty_flag() in its only user
      memory: unfold cpu_physical_memory_set_dirty() in its only user
      memory: unfold cpu_physical_memory_set_dirty_flag()
      memory: make cpu_physical_memory_get_dirty() the main function
      memory: cpu_physical_memory_get_dirty() is used as returning a bool
      memory: s/mask/clear/ cpu_physical_memory_mask_dirty_range
      memory: use find_next_bit() to find dirty bits
      memory: cpu_physical_memory_set_dirty_range() now uses bitmap operations
      memory: cpu_physical_memory_clear_dirty_range() now uses bitmap operations

 cputlb.c                       |  4 +-
 exec.c                         | 41 ++++++++++--------
 include/exec/cpu-all.h         |  4 +-
 include/exec/cpu-common.h      |  4 --
 include/exec/memory-internal.h | 94 ++++++++++++++++++------------------------
 include/exec/memory.h          | 10 ++---
 include/qemu/bitmap.h          |  9 ++++
 memory.c                       | 12 +++---
 8 files changed, 88 insertions(+), 90 deletions(-)