[Qemu-devel] [PATCH v3 0/9] Migration: Remove copying of guest ram pages

[Orit Wasserman]

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 writev to send the iovec.
writev was chosen (as apposed to sendmsg) because it supprts non socket fds.
  
Guest memory pages are not copied by calling a new function 
qemu_put_buffer_no_copy.
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.
Another improvement is changing qemu_putbe64/32/16 to create a single
buffer instead of several byte sized buffer.

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

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 (9):
  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
  More optimized qemu_put_be64/32/16
  Add qemu_put_buffer_no_copy
  Use qemu_put_buffer_no_copy for guest memory pages
  coalesce adjacent iovecs

 arch_init.c                   |   2 +-
 include/migration/qemu-file.h |  12 ++++
 savevm.c                      | 127 ++++++++++++++++++++++++++++++++++--------
 3 files changed, 116 insertions(+), 25 deletions(-)

-- 
1.7.11.7