Message ID | 20220331150857.74406-1-peterx@redhat.com (mailing list archive) |
---|---|
Headers | show |
Series | migration: Postcopy Preemption | expand |
* Peter Xu (peterx@redhat.com) wrote: > This is v4 of postcopy preempt series. It can also be found here: > > https://github.com/xzpeter/qemu/tree/postcopy-preempt > > RFC: https://lore.kernel.org/qemu-devel/20220119080929.39485-1-peterx@redhat.com > V1: https://lore.kernel.org/qemu-devel/20220216062809.57179-1-peterx@redhat.com > V2: https://lore.kernel.org/qemu-devel/20220301083925.33483-1-peterx@redhat.com > V3: https://lore.kernel.org/qemu-devel/20220330213908.26608-1-peterx@redhat.com I've queued: migration: Allow migrate-recover to run multiple times migration: Move channel setup out of postcopy_try_recover() migration: Export ram_load_postcopy() migration: Move migrate_allow_multifd and helpers into migration.c migration: Add pss.postcopy_requested status migration: Drop multifd tls_hostname cache migration: Postpone releasing MigrationState.hostname > v4: > - Fix a double-free on params.tls-creds when quitting qemu > - Reorder patches to satisfy per-commit builds > > v3: > - Rebased to master since many patches landed > - Fixed one bug on postcopy recovery when preempt enabled, this is only > found when I test with TLS+recovery, because TLS changed the timing. > - Dropped patch: > "migration: Fail postcopy preempt with TLS for now" > - Added patches for TLS: > - "migration: Postpone releasing MigrationState.hostname" > - "migration: Drop multifd tls_hostname cache" > - "migration: Enable TLS for preempt channel" > - "migration: Export tls-[creds|hostname|authz] params to cmdline too" > - "tests: Add postcopy tls migration test" > - "tests: Add postcopy tls recovery migration test" > - Added two more tests to the preempt test patch (tls, tls+recovery) > > Abstract > ======== > > This series added a new migration capability called "postcopy-preempt". It can > be enabled when postcopy is enabled, and it'll simply (but greatly) speed up > postcopy page requests handling process. > > Below are some initial postcopy page request latency measurements after the > new series applied. > > For each page size, I measured page request latency for three cases: > > (a) Vanilla: the old postcopy > (b) Preempt no-break-huge: preempt enabled, x-postcopy-preempt-break-huge=off > (c) Preempt full: preempt enabled, x-postcopy-preempt-break-huge=on > (this is the default option when preempt enabled) > > Here x-postcopy-preempt-break-huge parameter is just added in v2 so as to > conditionally disable the behavior to break sending a precopy huge page for > debugging purpose. So when it's off, postcopy will not preempt precopy > sending a huge page, but still postcopy will use its own channel. > > I tested it separately to give a rough idea on which part of the change > helped how much of it. The overall benefit should be the comparison > between case (a) and (c). > > |-----------+---------+-----------------------+--------------| > | Page size | Vanilla | Preempt no-break-huge | Preempt full | > |-----------+---------+-----------------------+--------------| > | 4K | 10.68 | N/A [*] | 0.57 | > | 2M | 10.58 | 5.49 | 5.02 | > | 1G | 2046.65 | 933.185 | 649.445 | > |-----------+---------+-----------------------+--------------| > [*]: This case is N/A because 4K page does not contain huge page at all > > [1] https://github.com/xzpeter/small-stuffs/blob/master/tools/huge_vm/uffd-latency.bpf > > TODO List > ========= > > Avoid precopy write() blocks postcopy > ------------------------------------- > > I didn't prove this, but I always think the write() syscalls being blocked > for precopy pages can affect postcopy services. If we can solve this > problem then my wild guess is we can further reduce the average page > latency. > > Two solutions at least in mind: (1) we could have made the write side of > the migration channel NON_BLOCK too, or (2) multi-threads on send side, > just like multifd, but we may use lock to protect which page to send too > (e.g., the core idea is we should _never_ rely anything on the main thread, > multifd has that dependency on queuing pages only on main thread). > > That can definitely be done and thought about later. > > Multi-channel for preemption threads > ------------------------------------ > > Currently the postcopy preempt feature use only one extra channel and one > extra thread on dest (no new thread on src QEMU). It should be mostly good > enough for major use cases, but when the postcopy queue is long enough > (e.g. hundreds of vCPUs faulted on different pages) logically we could > still observe more delays in average. Whether growing threads/channels can > solve it is debatable, but sounds worthwhile a try. That's yet another > thing we can think about after this patchset lands. > > Logically the design provides space for that - the receiving postcopy > preempt thread can understand all ram-layer migration protocol, and for > multi channel and multi threads we could simply grow that into multile > threads handling the same protocol (with multiple PostcopyTmpPage). The > source needs more thoughts on synchronizations, though, but it shouldn't > affect the whole protocol layer, so should be easy to keep compatible. > > Please review, thanks. > > Peter Xu (19): > migration: Postpone releasing MigrationState.hostname > migration: Drop multifd tls_hostname cache > migration: Add pss.postcopy_requested status > migration: Move migrate_allow_multifd and helpers into migration.c > migration: Export ram_load_postcopy() > migration: Move channel setup out of postcopy_try_recover() > migration: Allow migrate-recover to run multiple times > migration: Add postcopy-preempt capability > migration: Postcopy preemption preparation on channel creation > migration: Postcopy preemption enablement > migration: Postcopy recover with preempt enabled > migration: Create the postcopy preempt channel asynchronously > migration: Parameter x-postcopy-preempt-break-huge > migration: Add helpers to detect TLS capability > migration: Export tls-[creds|hostname|authz] params to cmdline too > migration: Enable TLS for preempt channel > tests: Add postcopy tls migration test > tests: Add postcopy tls recovery migration test > tests: Add postcopy preempt tests > > migration/channel.c | 11 +- > migration/migration.c | 218 ++++++++++++++++++++------ > migration/migration.h | 52 ++++++- > migration/multifd.c | 36 +---- > migration/multifd.h | 4 - > migration/postcopy-ram.c | 190 ++++++++++++++++++++++- > migration/postcopy-ram.h | 11 ++ > migration/qemu-file.c | 27 ++++ > migration/qemu-file.h | 1 + > migration/ram.c | 288 +++++++++++++++++++++++++++++++++-- > migration/ram.h | 3 + > migration/savevm.c | 49 ++++-- > migration/socket.c | 22 ++- > migration/socket.h | 1 + > migration/trace-events | 15 +- > qapi/migration.json | 8 +- > tests/qtest/migration-test.c | 113 ++++++++++++-- > 17 files changed, 918 insertions(+), 131 deletions(-) > > -- > 2.32.0 > >