Hi, In this v4:
- Added support for 'fd:'. With fixed-ram, that comes free by the existing routing to file.c. With multifd I added a loop to create the channels. - Dropped support for direct-io with fixed-ram _without_ multifd. This is something I said I would do for this version, but I had to drop it because performance is really bad. I think the single-threaded precopy code cannot cope with the extra latency/synchronicity of O_DIRECT. - Dropped QIOTask related changes. The file migration now calls multifd_channel_connect() directly. Any error can now be returned all the way up to migrate_fd_connect(). We can also skip the channels_created semaphore logic when using fixed-ram. - Moved the pwritev_read_contiguous code into a migration-specific file and dropped the write_base trick. - Reduced the number of syncs to just one every ram iteration and one at the end on the send side; and a single one at the end on the recv side. The EOS flag cannot be skipped because it is used in control flow at ram_load_precopy. The rest are minor changes, I have noted them in the patches themselves. CI run: https://gitlab.com/farosas/qemu/-/pipelines/1183853433 Series structure ================ This series enables fixed-ram in steps: 0) Cleanups [1-5] 1) QIOChannel interfaces [6-10] 2) Fixed-ram format for precopy [11-15] 3) Multifd adaptation without packets [16-19] 4) Fixed-ram format for multifd [20-26] 5) Direct-io generic support [27] 6) Direct-io for fixed-ram multifd with file: URI [28-29] 7) Fdset interface for fixed-ram multifd [30-34] The majority of changes for this version are at step 3 due to the rebase on top of the recent multifd cleanups. Please take a look at the later patches in the series, step 5 onwards. About fixed-ram =============== Fixed-ram is a new stream format for the RAM section designed to supplement the existing ``file:`` migration and make it compatible with ``multifd``. This enables parallel migration of a guest's RAM to a file. The core of the feature is to ensure that each RAM page has a specific offset in the resulting migration file. This enables the ``multifd`` threads to write exclusively to those offsets even if the guest is constantly dirtying pages (i.e. live migration). Another benefit is that the resulting file will have a bounded size, since pages which are dirtied multiple times will always go to a fixed location in the file, rather than constantly being added to a sequential stream. Having the pages at fixed offsets also allows the usage of O_DIRECT for save/restore of the migration stream as the pages are ensured to be written respecting O_DIRECT alignment restrictions. Latest numbers ============== => guest: 128 GB RAM - 120 GB dirty - 1 vcpu in tight loop dirtying memory => host: 128 CPU AMD EPYC 7543 - 2 NVMe disks in RAID0 (8586 MiB/s) - xfs => pinned vcpus w/ NUMA shortest distances - average of 3 runs - results from query-migrate non-live | time (ms) pages/s mb/s MB/s -------------------+----------------------------------- file | 110512 256258 9549 1193 + bg-snapshot | 245660 119581 4303 537 -------------------+----------------------------------- fixed-ram | 157975 216877 6672 834 + multifd 8 ch. | 95922 292178 10982 1372 + direct-io | 23268 1936897 45330 5666 ------------------------------------------------------- live | time (ms) pages/s mb/s MB/s -------------------+----------------------------------- file | - - - - (file grew 4x the VM size) + bg-snapshot | 357635 141747 2974 371 -------------------+----------------------------------- fixed-ram | - - - - (no convergence in 5 min) + multifd 8 ch. | 230812 497551 14900 1862 + direct-io | 27475 1788025 46736 5842 ------------------------------------------------------- Previous versions of this patchset have shown performance closer to disk saturation, but due to the query-migrate bug[1] it's hard to be confident in the previous numbers. I don't discard the possibility of a performance regression, but for now I can't spot anything that could have caused it. 1- https://lore.kernel.org/r/20240219194457.26923-1-faro...@suse.de v3: https://lore.kernel.org/r/20231127202612.23012-1-faro...@suse.de v2: https://lore.kernel.org/r/20231023203608.26370-1-faro...@suse.de v1: https://lore.kernel.org/r/20230330180336.2791-1-faro...@suse.de Fabiano Rosas (31): docs/devel/migration.rst: Document the file transport tests/qtest/migration: Rename fd_proto test tests/qtest/migration: Add a fd + file test migration/multifd: Remove p->quit from recv side migration/multifd: Release recv sem_sync earlier io: fsync before closing a file channel migration/qemu-file: add utility methods for working with seekable channels migration/ram: Introduce 'fixed-ram' migration capability migration: Add fixed-ram URI compatibility check migration/ram: Add outgoing 'fixed-ram' migration migration/ram: Add incoming 'fixed-ram' migration tests/qtest/migration: Add tests for fixed-ram file-based migration migration/multifd: Rename MultiFDSend|RecvParams::data to compress_data migration/multifd: Decouple recv method from pages migration/multifd: Allow multifd without packets migration/multifd: Allow receiving pages without packets migration/multifd: Add outgoing QIOChannelFile support migration/multifd: Add incoming QIOChannelFile support migration/multifd: Prepare multifd sync for fixed-ram migration migration/multifd: Support outgoing fixed-ram stream format migration/multifd: Support incoming fixed-ram stream format migration/multifd: Add fixed-ram support to fd: URI tests/qtest/migration: Add a multifd + fixed-ram migration test migration: Add direct-io parameter migration/multifd: Add direct-io support tests/qtest/migration: Add tests for file migration with direct-io monitor: Honor QMP request for fd removal immediately monitor: Extract fdset fd flags comparison into a function monitor: fdset: Match against O_DIRECT migration: Add support for fdset with multifd + file tests/qtest/migration: Add a test for fixed-ram with passing of fds Nikolay Borisov (3): io: add and implement QIO_CHANNEL_FEATURE_SEEKABLE for channel file io: Add generic pwritev/preadv interface io: implement io_pwritev/preadv for QIOChannelFile docs/devel/migration/features.rst | 1 + docs/devel/migration/fixed-ram.rst | 137 +++++++++ docs/devel/migration/main.rst | 22 ++ include/exec/ramblock.h | 13 + include/io/channel.h | 83 ++++++ include/migration/qemu-file-types.h | 2 + include/qemu/bitops.h | 13 + include/qemu/osdep.h | 2 + io/channel-file.c | 69 +++++ io/channel.c | 58 ++++ migration/fd.c | 30 ++ migration/fd.h | 1 + migration/file.c | 258 +++++++++++++++- migration/file.h | 9 + migration/migration-hmp-cmds.c | 11 + migration/migration.c | 68 ++++- migration/multifd-zlib.c | 26 +- migration/multifd-zstd.c | 26 +- migration/multifd.c | 436 +++++++++++++++++++++------- migration/multifd.h | 27 +- migration/options.c | 66 +++++ migration/options.h | 2 + migration/qemu-file.c | 106 +++++++ migration/qemu-file.h | 6 + migration/ram.c | 333 ++++++++++++++++++++- migration/ram.h | 1 + migration/savevm.c | 1 + monitor/fds.c | 27 +- qapi/migration.json | 24 +- tests/qtest/migration-helpers.c | 42 +++ tests/qtest/migration-helpers.h | 1 + tests/qtest/migration-test.c | 303 ++++++++++++++++++- util/osdep.c | 9 + 33 files changed, 2041 insertions(+), 172 deletions(-) create mode 100644 docs/devel/migration/fixed-ram.rst -- 2.35.3
