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[Qemu-devel] [PATCH v3 00/29] Dirty bitmap atomic access and optimizatio

From: Paolo Bonzini
Subject: [Qemu-devel] [PATCH v3 00/29] Dirty bitmap atomic access and optimizations
Date: Tue, 26 May 2015 18:54:36 +0200

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.

This patch series does the following optimizations and cleanups:

1) it lets KVM code treat migration as "just another dirty bitmap
client" instead of needing the special global_log_start/stop callbacks.
These remain in use in Xen and vhost.  This removes code and avoids
bugs such as the one fixed in commit 4cc856f (kvm-all: Sync dirty-bitmap
from kvm before kvm destroy the corresponding dirty_bitmap, 2015-04-02).

2) it avoids modifications to unused dirty bitmaps: code if TCG
is disabled, migration if no migration is in progress, VGA for
regions other than VRAM.

and on top of this makes dirty bitmap access atomic.  I'm not including
the patch to make the migration thread synchronize the bitmap outside
the big QEMU lock (thus removing the last source of jitter during the
RAM copy phase of migration) but it is also enabled by these patches.

Patches 1-4 are cleanups to DIRTY_MEMORY_VGA users.

Patches 5-12 are the first cleanup (KVM treats migration as just
another client).  Patches 13-14 are a simple optimization that is enabled
by these patches.

Patches 15-18 are bonus cleanups to translate-all.c's dirty memory
tracking for TCG.

Patches 19-22 are the second cleanup (avoid modifications to unused
dirty bitmaps).

Patches 23-28 are Stefan's patches for atomic access to the dirty
bitmap, which has no performance impact in the common case thanks to
the previous work.

Patch 29 is an unrelated strengthening of assertions, that mst spotted
while reviewing v1.

v2->v3: 22 patches reviewed by Fam
        fixed tcx24_update_display (patch 4, Fam)
        fixed comments (patch 5, Fam)
        improved commit messages (patches 7/10/11, Fam)
        fixed logic for full word loops (patches 23/24, Fam)
        avoid duplicated ~(ram_addr_t)0 constant (patch 29, Fam)

v1->v2: completed work on removing global_start/global_stop from KVM

        extra spelunking of TCG history so that the exec.c code
        makes more sense

        extra splitting of patches (Stefan)

        keep memory_region_is_logging and memory_region_get_dirty_log_mask
        APIs separate (mst)

Paolo Bonzini (23):
  memory: the only dirty memory flag for users is DIRTY_MEMORY_VGA
  g364fb: remove pointless call to memory_region_set_coalescing
  display: enable DIRTY_MEMORY_VGA tracking explicitly
  display: add memory_region_sync_dirty_bitmap calls
  memory: differentiate memory_region_is_logging and
  memory: prepare for multiple bits in the dirty log mask
  framebuffer: check memory_region_is_logging
  ui/console: remove dpy_gfx_update_dirty
  memory: track DIRTY_MEMORY_CODE in mr->dirty_log_mask
  kvm: accept non-mapped memory in kvm_dirty_pages_log_change
  memory: include DIRTY_MEMORY_MIGRATION in the dirty log mask
  kvm: remove special handling of DIRTY_MEMORY_MIGRATION in the dirty
    log mask
  ram_addr: tweaks to xen_modified_memory
  exec: use memory_region_get_dirty_log_mask to optimize dirty tracking
  exec: move functions to translate-all.h
  translate-all: remove unnecessary argument to tb_invalidate_phys_range
  cputlb: remove useless arguments to tlb_unprotect_code_phys, rename
  translate-all: make less of tb_invalidate_phys_page_range depend on
  exec: pass client mask to cpu_physical_memory_set_dirty_range
  exec: invert return value of cpu_physical_memory_get_clean, rename
  exec: only check relevant bitmaps for cleanliness
  memory: do not touch code dirty bitmap unless TCG is enabled
  memory: use mr->ram_addr in "is this RAM?" assertions

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                  |  46 +--------------
 cputlb.c                     |   7 +--
 exec.c                       |  99 +++++++++++++++----------------
 hw/display/cg3.c             |   2 +
 hw/display/exynos4210_fimd.c |  20 ++++---
 hw/display/framebuffer.c     |   4 ++
 hw/display/g364fb.c          |   3 +-
 hw/display/sm501.c           |   2 +
 hw/display/tcx.c             |   3 +
 hw/display/vmware_vga.c      |   2 +-
 hw/virtio/dataplane/vring.c  |   2 +-
 hw/virtio/vhost.c            |   9 ++-
 include/exec/cputlb.h        |   3 +-
 include/exec/exec-all.h      |   6 +-
 include/exec/memory.h        |  25 ++++++--
 include/exec/ram_addr.h      | 138 ++++++++++++++++++++++++++++---------------
 include/qemu/bitmap.h        |   4 ++
 include/qemu/bitops.h        |  14 +++++
 include/ui/console.h         |   4 --
 kvm-all.c                    |  77 ++++++------------------
 linux-user/mmap.c            |   7 ++-
 memory.c                     |  81 +++++++++++++++++--------
 translate-all.c              |  20 +++----
 translate-all.h              |   7 +++
 ui/console.c                 |  61 -------------------
 user-exec.c                  |   1 +
 util/bitmap.c                |  83 ++++++++++++++++++++++++++
 xen-hvm.c                    |  22 ++++---
 28 files changed, 408 insertions(+), 344 deletions(-)


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