On 18/07/2023 18:46, Jason Gunthorpe wrote:
On Sun, Jul 16, 2023 at 11:15:35AM +0300, Avihai Horon wrote:
Hi all,
The first patch in this series adds a small optimization to VFIO
migration by moving the STOP_COPY->STOP transition to
vfio_save_cleanup(). Testing with a ConnectX-7 VFIO device showed that
this can reduce downtime by up to 6%.
The rest of the series adds P2P support for VFIO migration.
VFIO migration uAPI defines an optional intermediate P2P quiescent
state. While in the P2P quiescent state, P2P DMA transactions cannot be
initiated by the device, but the device can respond to incoming ones.
Additionally, all outstanding P2P transactions are guaranteed to have
been completed by the time the device enters this state.
For clarity it is "all outstanding DMA transactions are guarenteed to
have been completed" - the device has no idea if something is P2P or
not.
The uAPI states that [1]: "If the device can identify P2P
transactionsthen it can stop only P2P DMA, otherwise it must stop all DMA.".
So I will stick to the uAPI definition.
[1]
https://elixir.bootlin.com/linux/v6.5-rc1/source/include/uapi/linux/vfio.h#L1032
The purpose of this state is to support migration of multiple devices
that are doing P2P transactions between themselves.
s/are/might/
Sure, will change it.
Thanks!
