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[Qemu-devel] [PATCH v4 0/8] Migration: Remove copying of guest ram pages
From: |
Orit Wasserman |
Subject: |
[Qemu-devel] [PATCH v4 0/8] Migration: Remove copying of guest ram pages |
Date: |
Thu, 21 Mar 2013 20:34:30 +0200 |
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
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 (8):
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
coalesce adjacent iovecs
arch_init.c | 2 +-
include/migration/qemu-file.h | 12 +++++
savevm.c | 101 +++++++++++++++++++++++++++++++++++-------
3 files changed, 99 insertions(+), 16 deletions(-)
--
1.7.11.7
- [Qemu-devel] [PATCH v4 0/8] Migration: Remove copying of guest ram pages,
Orit Wasserman <=
[Qemu-devel] [PATCH v4 3/8] Update bytes_xfer in qemu_put_byte, Orit Wasserman, 2013/03/21
[Qemu-devel] [PATCH v4 4/8] Store the data to send also in iovec, Orit Wasserman, 2013/03/21
[Qemu-devel] [PATCH v4 5/8] Use writev ops if available, Orit Wasserman, 2013/03/21
[Qemu-devel] [PATCH v4 6/8] Add qemu_put_buffer_async, Orit Wasserman, 2013/03/21