Re: [PATCH v10 0/7] MSG_ZEROCOPY + multifd

[Leonardo Bras Soares Passos]

On Thu, Apr 28, 2022 at 11:08 AM Dr. David Alan Gilbert
<dgilbert@redhat.com> wrote:
>
> * Leonardo Bras (leobras@redhat.com) wrote:
> > 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 implements io_writev flags and io_flush() on QIOChannelSocket,
> > making use of MSG_ZEROCOPY on Linux.
> >
> > Patch #3 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 #4 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 #5 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 #6 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 #7 Makes use of QIOChannelSocket zero_copy implementation on
> > nocomp multifd migration.
>
> Queued.
>
> > 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.
>
> Nice.
>
> > 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
>
> That configuration is particularly interesting because while it's a big
> machine with lots of cores, the individual cores are clocked relatively
> slowly; also having lots of cores probably means they're all fighting
> over memory bandwidth, so the less copies the better.
>
> Dave
>

Thanks Dave!

Best regards,
Leo

> > - VM configuration:
> >   - 28 VCPUs
> >   - 512GB RAM
> >
> >
> > ---
> > 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 (7):
> >   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)
> >
> >  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                 | 110 +++++++++++++++++++++++++++-
> >  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                 |  75 +++++++++++++++----
> >  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 +
> >  23 files changed, 379 insertions(+), 44 deletions(-)
> >
> > --
> > 2.36.0
> >
> > From c6fda6f8fb29ceeaf4d36f3787b85196e9bb281f Mon Sep 17 00:00:00 2001
> > From: Leonardo Bras <leobras@redhat.com>
> > Date: Mon, 25 Apr 2022 17:45:14 -0300
> > MIME-Version: 1.0
> > Content-Type: text/plain; charset=UTF-8
> > Content-Transfer-Encoding: 8bit
> > To: "Marc-André Lureau" <marcandre.lureau@redhat.com>,Paolo Bonzini 
> > <pbonzini@redhat.com>,Elena Ufimtseva 
> > <elena.ufimtseva@oracle.com>,Jagannathan Raman <jag.raman@oracle.com>,John 
> > G Johnson <john.g.johnson@oracle.com>,"Daniel P. Berrangé" 
> > <berrange@redhat.com>,Juan Quintela <quintela@redhat.com>,"Dr. David Alan 
> > Gilbert" <dgilbert@redhat.com>,Eric Blake <eblake@redhat.com>,Markus 
> > Armbruster <armbru@redhat.com>,Fam Zheng <fam@euphon.net>,Peter Xu 
> > <peterx@redhat.com>
> > Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org,
> >
> >
> > Leonardo Bras (7):
> >   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)
> >
> >  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                 | 110 +++++++++++++++++++++++++++-
> >  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                 |  72 +++++++++++++++---
> >  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 +
> >  23 files changed, 377 insertions(+), 43 deletions(-)
> >
> > --
> > 2.36.0
> >
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>