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[Qemu-devel] [PATCH 00/22] Dirty bitmap atomic access and optimizations

From: Paolo Bonzini
Subject: [Qemu-devel] [PATCH 00/22] Dirty bitmap atomic access and optimizations
Date: Thu, 26 Mar 2015 18:38:18 +0100

QEMU is currently accessing the dirty bitmaps very liberally,
which is understandable since the accesses are cheap.  This is
however not good for squeezing maximum performance out of dataplane,
and is also not good if the accesses become more expensive---as is
the case when they use atomic primitives.

Patches 1-2 make acpi-build.h only use public memory APIs.

Patches 3-7 optimize access to the VGA dirty bitmap, by restricting
it to video RAM only.

Patches 8-15 optimize access to the code and migration bitmaps,
by tracking them respectively if TCG is enabled and if migration
is in progress.  Note that the first iteration of migration already
does not look at the migration bitmap (commit 70c8652, migration:
do not search dirty pages in bulk stage, 2013-03-26).

Patches 16-21 are Stefan's patches to convert bitmap access to use
atomic primitives.

While the main purpose of these patches is a working dirty bitmap
for dataplane (and possibly multithreaded TCG), there's something
that they are immediately useful for: patch 22 makes the migration
thread synchronize the bitmap outside the big QEMU lock, thus
removing the last source of jitter during the RAM copy phase of

Please review and test! (it's available as branch "atomic-dirty"
on my github repository)  In particular, I suspect that the
postcopy patches might be good at finding bugs.


Paolo Bonzini (16):
  memory: add memory_region_ram_resize
  acpi-build: remove dependency from ram_addr.h
  memory: the only dirty memory flag for users is DIRTY_MEMORY_VGA
  display: enable DIRTY_MEMORY_VGA tracking explicitly
  memory: return bitmap from memory_region_is_logging
  framebuffer: check memory_region_is_logging
  ui/console: check memory_region_is_logging
  memory: track DIRTY_MEMORY_CODE in mr->dirty_log_mask
  memory: return DIRTY_MEMORY_MIGRATION from memory_region_is_logging
  ram_addr: tweaks to xen_modified_memory
  exec: simplify notdirty_mem_write
  exec: use memory_region_is_logging to optimize dirty tracking
  exec: pass client mask to cpu_physical_memory_set_dirty_range
  exec: only check relevant bitmaps for cleanliness
  memory: do not touch code dirty bitmap unless TCG is enabled
  migration: run bitmap sync outside iothread lock

Stefan Hajnoczi (6):
  bitmap: add atomic set functions
  bitmap: add atomic test and clear
  memory: use atomic ops for setting dirty memory bits
  migration: move dirty bitmap sync to ram_addr.h
  memory: replace cpu_physical_memory_reset_dirty() with test-and-clear
  memory: make cpu_physical_memory_sync_dirty_bitmap() fully atomic

 arch_init.c                  |  56 +++----------------
 cputlb.c                     |   4 +-
 exec.c                       | 103 ++++++++++++++++------------------
 hw/core/loader.c             |   8 +--
 hw/display/cg3.c             |   1 +
 hw/display/exynos4210_fimd.c |   7 ++-
 hw/display/framebuffer.c     |  23 ++++++--
 hw/display/g364fb.c          |   2 +-
 hw/display/sm501.c           |   1 +
 hw/display/tcx.c             |   1 +
 hw/display/vmware_vga.c      |   2 +-
 hw/i386/acpi-build.c         |  36 ++++++------
 hw/virtio/vhost.c            |   3 +-
 include/exec/memory.h        |  27 +++++++--
 include/exec/ram_addr.h      | 128 ++++++++++++++++++++++++++++---------------
 include/hw/loader.h          |   8 ++-
 include/qemu/bitmap.h        |   4 ++
 include/qemu/bitops.h        |  14 +++++
 kvm-all.c                    |   3 +-
 memory.c                     |  34 ++++++++----
 ui/console.c                 |  14 +++--
 util/bitmap.c                |  78 ++++++++++++++++++++++++++
 xen-hvm.c                    |   3 +-
 23 files changed, 356 insertions(+), 204 deletions(-)


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