[Qemu-devel] [PATCH v5 0/7] Migration: Remove copying of guest ram pages

[Orit Wasserman <owasserm@redhat.com>]

In migration all data is copied to a static buffer in QEMUFile,
this hurts our network bandwidth and CPU usage especially with large guests.
We switched to iovec for storing different buffers to send (even a byte field is
considered as a buffer) and use sendmsg to send the iovec.
Adjacent iovecs are coalesced to create a bigger buffer instead of many small
buffers.
  
Guest memory pages are not copied by calling a new function
qemu_put_buffer_async.
The page header data and device state data are still copied into the static
buffer. This data consists of a lot of bytes and integer fields and the static
buffer is used to store it during batching.

git repository: git://github.com/oritwas/qemu.git sendv_v2

Changes from v4:
return ssize_t for writev_buffer ops.
Fix other Eric's comments.
Squash patch 8 (coalesce adjacent iovecs) into patch 4.

Changes from v3:
Use a variable for iov_size
Change f->bytes_xfer +=1 to f->bytes_xfer++
Remove unneeded "More optimized qemu_put_be64/32/16" patch
Move code to the right patch
Rename qemu_put_buffer_no_copy to qemu_put_buffer_async
Use function for updating the iovec that detect adjacent iovecs and coalesce
them.

Change from v2:
Always send data for the iovec even if writev_buffer is not implemented.
Coalesce adjacent iovecs to create one big buffer from small adjacent buffer.

Changes from v1:
Use iov_send for socket.
Make writev_buffer optional and if it is not implemented use put_buffer

Future work: Make number of iovec changeable

Orit Wasserman (7):
  Add QemuFileWritevBuffer QemuFileOps
  Add socket_writev_buffer function
  Update bytes_xfer in qemu_put_byte
  Store the data to send also in iovec
  Use writev ops if available
  Add qemu_put_buffer_async
  Use qemu_put_buffer_async for guest memory pages

 arch_init.c                   |   2 +-
 include/migration/qemu-file.h |  12 +++++
 savevm.c                      | 103 +++++++++++++++++++++++++++++++++++-------
 3 files changed, 100 insertions(+), 17 deletions(-)

-- 
1.7.11.7