This patch series intends to enable MSG_ZEROCOPY in QIOChannel, and make
use of it for multifd migration performance improvement, by reducing cpu
usage.
Patch #1 creates new callbacks for QIOChannel, allowing the implementation
of zero copy writing.
Patch #2 reworks qio_channel_socket_writev() so it accepts flags for
that are later passed to sendmsg().
Patch #3 implements writev_zero_copy and flush_zero_copy on QIOChannelSocket,
making use of MSG_ZEROCOPY on Linux.
Patch #4 adds a "zero_copy" migration property, only available with
CONFIG_LINUX, and compiled-out in any other architectures.
This migration property has to be enabled before multifd migration starts.
Patch #5 adds a helper function that allows to see if TLS is going to be used.
This helper will be later used in patch #6.
Patch #6 Makes use of QIOChannelSocket zero_copy implementation on
nocomp multifd migration.
Results:
In preliminary tests, the resource usage of __sys_sendmsg() reduced 15 times,
and the overall migration took 13-22% less time, based in synthetic cpu
workload.
In further tests, it was noted that, on multifd migration with 8 channels:
- On idle hosts, migration time reduced in 10% to 21%.
- On hosts busy with heavy cpu stress (1 stress thread per cpu, but
not cpu-pinned) migration time reduced in ~25% by enabling zero-copy.
- On hosts with heavy cpu-pinned workloads (1 stress thread per cpu,
cpu-pinned), migration time reducted in ~66% by enabling zero-copy.
Above tests setup:
- Sending and Receiving hosts:
- CPU : Intel(R) Xeon(R) Platinum 8276L CPU @ 2.20GHz (448 CPUS)
- Network card: E810-C (100Gbps)
- >1TB RAM
- QEMU: Upstream master branch + This patchset
- Linux: Upstream v5.15
- VM configuration:
- 28 VCPUs
- 512GB RAM
---
Changes since v5:
- flush_zero_copy now returns -1 on fail, 0 on success, and 1 when all
processed writes were not able to use zerocopy in kernel.
- qio_channel_socket_poll() removed, using qio_channel_wait() instead
- ENOBUFS is now processed inside qio_channel_socket_writev_flags()
- Most zerocopy parameter validation moved to migrate_params_check(),
leaving only feature test to socket_outgoing_migration() callback
- Naming went from *zerocopy to *zero_copy or *zero-copy, due to QAPI/QMP
preferences
- Improved docs
Changes since v4:
- 3 patches got splitted in 6
- Flush is used for syncing after each iteration, instead of only at the end
- If zerocopy is not available, fail in connect instead of failing on write
- 'multifd-zerocopy' property renamed to 'zerocopy'
- Fail migrations that don't support zerocopy, if it's enabled.
- Instead of checking for zerocopy at each write, save the flags in
MultiFDSendParams->write_flags and use them on write
- Reorganized flag usage in QIOChannelSocket
- A lot of typos fixed
- More doc on buffer restrictions
Changes since v3:
- QIOChannel interface names changed from io_async_{writev,flush} to
io_{writev,flush}_zerocopy
- Instead of falling back in case zerocopy is not implemented, return
error and abort operation.
- Flush now waits as long as needed, or return error in case anything
goes wrong, aborting the operation.
- Zerocopy is now conditional in multifd, being set by parameter
multifd-zerocopy
- Moves zerocopy_flush to multifd_send_sync_main() from multifd_save_cleanup
so migration can abort if flush goes wrong.
- Several other small improvements
Changes since v2:
- Patch #1: One more fallback
- Patch #2: Fall back to sync if fails to lock buffer memory in MSG_ZEROCOPY
send.
Changes since v1:
- Reimplemented the patchset using async_write + async_flush approach.
- Implemented a flush to be able to tell whenever all data was written.
Leonardo Bras (6):
QIOChannel: Add io_writev_zero_copy & io_flush_zero_copy callbacks
QIOChannelSocket: Add flags parameter for writing
QIOChannelSocket: Implement io_writev_zero_copy & io_flush_zero_copy
for CONFIG_LINUX
migration: Add zero-copy parameter for QMP/HMP for Linux
migration: Add migrate_use_tls() helper
multifd: Implement zero copy write in multifd migration
(multifd-zero-copy)
qapi/migration.json | 24 ++++++
include/io/channel-socket.h | 2 +
include/io/channel.h | 98 +++++++++++++++++++++---
migration/migration.h | 6 ++
migration/multifd.h | 4 +-
io/channel-socket.c | 145 +++++++++++++++++++++++++++++++++---
io/channel.c | 66 +++++++++++++---
migration/channel.c | 6 +-
migration/migration.c | 49 ++++++++++++
migration/multifd.c | 45 ++++++++---
migration/ram.c | 29 ++++++--
migration/socket.c | 6 ++
monitor/hmp-cmds.c | 6 ++
13 files changed, 434 insertions(+), 52 deletions(-)
--
2.33.1
