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 conditionally disables liburing in systems where linux/errqueue.h
conflict with liburing/compat.h (__kernel_timespec redefine)
Patch #2 creates new callbacks for QIOChannel, allowing the implementation
of zero copy writing.
Patch #3 implements io_writev flags and io_flush() on QIOChannelSocket,
making use of MSG_ZEROCOPY on Linux.
Patch #4 adds a "zero_copy_send" 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 #5.
Patch #6 changes multifd_send_sync_main() so it returns int instead of void.
The return value is used to understand if any error happened in the function,
allowing migration to possible fail earlier.
Patch #7 implements an workaround: The behavior introduced in d48c3a0445 is
hard to deal with in zerocopy, so a workaround is introduced to send the
header in a different syscall, without MSG_ZEROCOPY.
Patch #8 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 v12:
- New patch #1 added to solve an issue with Gitlab CI on alpine
- Removed unnecessary newline in patch #3 (previously #2)
- Removed incorrect commit change in roms/skiboot on patch #4
(previously #3)
Changes since v11:
- Patch #3 now wrap lines around column 75
- Patch #2 now introduce some #ifdefs instead of defining a
default value for MSG_ZEROCOPY and SO_ZEROCOPY
Changes since v10:
- Patch #2 was breaking build on systems with glibc < glibc-2.27,
and probably non-linux builds.
- Also on Patch #2, replaced bits/socket.h with sys/socket.h,
(thanks Peter Xu)
Changes since v9:
- Patch #6 got simplified and improved (thanks Daniel)
- Patch #7 got better comments (thanks Peter Xu)
Changes since v8:
- Inserted two new patches #5 & #6, previous patch #5 is now #7.
- Workaround an optimization introduced in d48c3a0445
- Removed unnecessary assert in qio_channel_writev_full_all
Changes since v7:
- Migration property renamed from zero-copy to zero-copy-send
- A few early tests added to help misconfigurations to fail earlier
- qio_channel_full*_flags() renamed back to qio_channel_full*()
- multifd_send_sync_main() reverted back to not receiving a flag,
so it always sync zero-copy when enabled.
- Improve code quality on a few points
Changes since v6:
- Remove io_writev_zero_copy(), and makes use of io_writev() new flags
to achieve the same results.
- Rename io_flush_zero_copy() to io_flush()
- Previous patch #2 became too small, so it was squashed in previous
patch #3 (now patch #2)
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 (8):
meson.build: Fix docker-test-build@alpine when including
linux/errqueue.h
QIOChannel: Add flags on io_writev and introduce io_flush callback
QIOChannelSocket: Implement io_writev zero copy flag & io_flush for
CONFIG_LINUX
migration: Add zero-copy-send parameter for QMP/HMP for Linux
migration: Add migrate_use_tls() helper
multifd: multifd_send_sync_main now returns negative on error
multifd: Send header packet without flags if zero-copy-send is enabled
multifd: Implement zero copy write in multifd migration
(multifd-zero-copy)
meson.build | 11 +++
qapi/migration.json | 24 ++++++
include/io/channel-socket.h | 2 +
include/io/channel.h | 38 ++++++++-
migration/migration.h | 6 ++
migration/multifd.h | 4 +-
chardev/char-io.c | 2 +-
hw/remote/mpqemu-link.c | 2 +-
io/channel-buffer.c | 1 +
io/channel-command.c | 1 +
io/channel-file.c | 1 +
io/channel-socket.c | 118 +++++++++++++++++++++++++++-
io/channel-tls.c | 1 +
io/channel-websock.c | 1 +
io/channel.c | 49 +++++++++---
migration/channel.c | 3 +-
migration/migration.c | 52 +++++++++++-
migration/multifd.c | 74 ++++++++++++++---
migration/ram.c | 29 +++++--
migration/rdma.c | 1 +
migration/socket.c | 12 ++-
monitor/hmp-cmds.c | 6 ++
scsi/pr-manager-helper.c | 2 +-
tests/unit/test-io-channel-socket.c | 1 +
24 files changed, 397 insertions(+), 44 deletions(-)
--
2.36.1
