| Message ID | 20241129122256.96778-1-ppandit@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Allow to enable multifd and postcopy migration together | expand |
On Fri, Nov 29, 2024 at 05:52:53PM +0530, Prasad Pandit wrote: > From: Prasad Pandit <pjp@fedoraproject.org> > > Hello, > > * Currently Multifd and Postcopy migration can not be used together. > QEMU shows "Postcopy is not yet compatible with multifd" message. > > When migrating guests with large (100's GB) RAM, Multifd threads > help to accelerate migration, but inability to use it with the > Postcopy mode delays guest start up on the destination side. > > * This patch series allows to enable both Multifd and Postcopy > migration together. Precopy and Multifd threads work during > the initial guest (RAM) transfer. When migration moves to the > Postcopy phase, Multifd threads are restrained and the Postcopy > threads start to request pages from the source side. > > * This series removes magic value (4-bytes) introduced in the > previous series for the Postcopy channel. And refactoring of > the 'ram_save_target_page' function is made independent of > the multifd & postcopy change. > > v1: https://lore.kernel.org/qemu-devel/20241126115748.118683-1-ppandit@redhat.com/T/#u > v0: https://lore.kernel.org/qemu-devel/20241029150908.1136894-1-ppandit@redhat.com/T/#u > > > Thank you. > --- > Prasad Pandit (3): > migration/multifd: move macros to multifd header > migration: refactor ram_save_target_page functions > migration: enable multifd and postcopy together Prasad, I saw that there's still discussion in the previous version, while this cover letter doesn't mention why it was ignored. Especially, at least to me, what Fabiano commented on simplifying the flush condition check makes senes to me to be addressed. Please cherish reviewer's feedback and time contributed, and let's finish the disucssion first before rushing for a new version. I'll try to join the discussion later too there. Meanwhile, before I read into any details, I found that all the tests I requested are still missing. Would you please consider adding them? My previous comment regarding to test is here: https://lore.kernel.org/qemu-devel/ZykJBq7ME5jgSzCA@x1n/ I listed exactly the minimum set of tests that I think we should have. In general, any migration new feature must have both doc updates and test coverage as long as applicable. Multifd still has its doc missing, which is unfortunate. We could have one doc prior to this work, but it can also be done later. OTOH on testing: this is not a new feature alone, but it's more dangerous than a new feature due to what I mentioned before, that postcopy needs atomicity on page movements, and multifd is completely against that from design POV due to NIC drivers being able to modify guest pages directly. It means multifd+postcopy bugs will be extremely hard to debug if we don't put it right first. So please be serious on the test coverage on this work. Thanks,
From: Prasad Pandit <pjp@fedoraproject.org> Hello, * Currently Multifd and Postcopy migration can not be used together. QEMU shows "Postcopy is not yet compatible with multifd" message. When migrating guests with large (100's GB) RAM, Multifd threads help to accelerate migration, but inability to use it with the Postcopy mode delays guest start up on the destination side. * This patch series allows to enable both Multifd and Postcopy migration together. Precopy and Multifd threads work during the initial guest (RAM) transfer. When migration moves to the Postcopy phase, Multifd threads are restrained and the Postcopy threads start to request pages from the source side. * This series removes magic value (4-bytes) introduced in the previous series for the Postcopy channel. And refactoring of the 'ram_save_target_page' function is made independent of the multifd & postcopy change. v1: https://lore.kernel.org/qemu-devel/20241126115748.118683-1-ppandit@redhat.com/T/#u v0: https://lore.kernel.org/qemu-devel/20241029150908.1136894-1-ppandit@redhat.com/T/#u Thank you. --- Prasad Pandit (3): migration/multifd: move macros to multifd header migration: refactor ram_save_target_page functions migration: enable multifd and postcopy together migration/migration.c | 90 +++++++++++++++++++++++--------------- migration/multifd-nocomp.c | 3 +- migration/multifd.c | 5 --- migration/multifd.h | 5 +++ migration/options.c | 5 --- migration/ram.c | 73 +++++++++---------------------- 6 files changed, 82 insertions(+), 99 deletions(-)