[Qemu-devel] [RFC 00/12] 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 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.

Orit Wasserman (12):
  Add iov_writev to use writev to send iovec (also for files)
  Add QemuFileWritevBuffer QemuFileOps
  Add socket_writev_buffer function
  Add stdio_writev_buffer function
  Add block_writev_buffer function
  Update bytes_xfer in qemu_put_byte
  Store the data to send also in iovec
  Use writev ops instead of put_buffer ops
  More optimized qemu_put_be64/32/16
  Add qemu_put_buffer_no_copy
  Use qemu_put_buffer_no_copy for guest memory pages
  Bye Bye put_buffer

 arch_init.c                   |   2 +-
 include/migration/qemu-file.h |  20 ++++---
 include/qemu/iov.h            |  12 ++++
 savevm.c                      | 130 +++++++++++++++++++++++++-----------------
 util/iov.c                    |  36 ++++++++++++
 5 files changed, 139 insertions(+), 61 deletions(-)

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1.7.11.7