| Message ID | 20220331150857.74406-1-peterx@redhat.com |
|---|---|
| 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 > >
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 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(-)