[Qemu-devel] [PATCH v5 0/4] Introduce bit-based phys_ram_dirty, and bit-based dirty page checker.

[Yoshiaki Tamura]

The dirty and non-dirty pages are checked one by one.  When most of the memory
is not dirty, checking the dirty and non-dirty pages by multiple page size
should be much faster than checking them one by one.  We introduced bit-based
phys_ram_dirty for VGA, CODE, MIGRATION, MASTER, and
cpu_physical_memory_get_dirty_range() for this purpose.
                                                                                
The following numbers show the speed up of bit-based phys_ram_dirty.  The speed
up grows when the number of rows, whose contents are 0, gets larger.

Test Environment:
CPU: 4x Intel Xeon Quad Core 2.66GHz
Mem size: 96GB

Host OS: CentOS (kernel 2.6.33)
Guest OS: Debian/GNU Linux lenny (kernel 2.6.26)
Guest Mem size: 512MB

Conditions of experiments are as follows:
Cond1: Guest OS periodically makes the 256MB continuous dirty pages.
Cond2: Guest OS periodically makes the 256MB dirty pages and non-dirty pages
in turn.
Cond3: Guest OS read 1GB file, which is bigger than memory.
Cond4: Guest OS write 1GB file, which is bigger than memory.

Experimental results:
Cond1: 5 ??? 83 times speed up
Cond2: 5 ??? 52 times speed up
Cond3: 5 ??? 132 times speed up
Cond4: 5 ??? 57 times speed up

Changes from v4 to v5 are:
- Rebased to HEAD (2b644fd0e737407133c88054ba498e772ce01f27)
- Use BITMAP_SIZE() in kvm_physical_sync_dirty_bitmap() (3/4)

Changes from v3 to v4 are:

- Merged {1,2,3}/6 to compile correctly.
- Fix setting bits after phys_ram_dirty allocation.
- renamed DIRTY_FLAG and DIRTY_IDX converter function.

Changes from v2 to v3 are:

- Change FLAGS value to (1,2,4,8), and add IDX (0,1,2,3)
- Use ffs to convert FLAGS to IDX.
- Add a helper function which takes IDX.
- Change the behavior of MASTER as a buffer.
- Change dirty bitmap access to a loop.
- Add brace after if ()

Yoshiaki Tamura (4):
  Modify DIRTY_FLAG value and introduce DIRTY_IDX to use as indexes of
    bit-based phys_ram_dirty.
  Introduce cpu_physical_memory_get_dirty_range().
  Use cpu_physical_memory_set_dirty_range() to update phys_ram_dirty.
  Use cpu_physical_memory_get_dirty_range() to check multiple dirty
    pages.

 arch_init.c   |   54 ++++++++++++++---------
 cpu-all.h     |  132 ++++++++++++++++++++++++++++++++++++++++++++++++---------
 exec.c        |   82 +++++++++++++++++++++++++++++++++--
 kvm-all.c     |   24 ++++------
 qemu-common.h |    3 +
 5 files changed, 234 insertions(+), 61 deletions(-)