[Qemu-devel] [PATCH v2 00/39] bitmap handling optimization

[Juan Quintela <quintela@redhat.com>]

Hi

[v2]
In this version:
- fixed all the comments from last versions (thanks Eric)
- kvm migration bitmap is synchronized using bitmap operations
- qemu bitmap -> migration bitmap is synchronized using bitmap operations
If bitmaps are not properly aligned, we fall back to old code.
Code survives virt-tests, so should be in quite good shape.

ToDo list:

- vga ram by default is not aligned in a page number multiple of 64,

  it could be optimized.  Kraxel?  It syncs the kvm bitmap at least 1
  a second or so? bitmap is only 2048 pages (16MB by default).
  We need to change the ram_addr only

- vga: still more, after we finish migration, vga code continues
  synchronizing the kvm bitmap on source machine.  Notice that there
  is no graphics client connected to the VGA.  Worth investigating?

- I haven't yet meassure speed differences on big hosts.  Vinod?

- Depending of performance, more optimizations to do.

- debugging printf's still on the code, just to see if we are taking
  (or not) the optimized paths.

And that is all.  Please test & comment.

Thanks, Juan.

[v1]
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 effective


The following changes since commit c2d30667760e3d7b81290d801e567d4f758825ca:

  rtc: remove dead SQW IRQ code (2013-11-05 20:04:03 -0800)

are available in the git repository at:

  git://github.com/juanquintela/qemu.git bitmap-v2.next

for you to fetch changes up to d91eff97e6f36612eb22d57c2b6c2623f73d3997:

  migration: synchronize memory bitmap 64bits at a time (2013-11-06 13:54:56 +0100)

----------------------------------------------------------------
Juan Quintela (39):
      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() always 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
      memory: s/dirty/clean/ in cpu_physical_memory_is_dirty()
      memory: make cpu_physical_memory_reset_dirty() take a length parameter
      memory: cpu_physical_memory_set_dirty_tracking() should return void
      memory: split cpu_physical_memory_* functions to its own include
      memory: unfold memory_region_test_and_clear()
      kvm: use directly cpu_physical_memory_* api for tracking dirty pages
      kvm: refactor start address calculation
      memory: move bitmap synchronization to its own function
      memory: syncronize kvm bitmap using bitmaps operations
      ram: split function that synchronizes a range
      migration: synchronize memory bitmap 64bits at a time

 arch_init.c                    |  57 ++++++++++++----
 cputlb.c                       |  10 +--
 exec.c                         |  75 ++++++++++-----------
 include/exec/cpu-all.h         |   4 +-
 include/exec/cpu-common.h      |   4 --
 include/exec/memory-internal.h |  84 ------------------------
 include/exec/memory-physical.h | 143 +++++++++++++++++++++++++++++++++++++++++
 include/exec/memory.h          |  10 +--
 include/qemu/bitmap.h          |   9 +++
 kvm-all.c                      |  28 ++------
 memory.c                       |  17 ++---
 11 files changed, 260 insertions(+), 181 deletions(-)
 create mode 100644 include/exec/memory-physical.h