In this version:
- attach more information in the cover letter.
- remove changes on virtio_load().
- add rcu_read_locked() to detect holding of rcu lock.
The duration of loading non-iterable vmstate accounts for a significant
portion of downtime (starting with the timestamp of source qemu stop and
ending with the timestamp of target qemu start). Most of the time is spent
committing memory region changes repeatedly.
This patch packs all the changes to memory region during the period of
loading non-iterable vmstate in a single memory transaction. With the
increase of devices, this patch will greatly improve the performance.
Here are the test1 results:
test info:
- Host
- Intel(R) Xeon(R) Platinum 8260 CPU
- NVIDIA Mellanox ConnectX-5
- VM
- 32 CPUs 128GB RAM VM
- 8 16-queue vhost-net device
- 16 4-queue vhost-user-blk device.
time of loading non-iterable vmstate downtime
before about 150 ms 740+ ms
after about 30 ms 630+ ms
(This result is different from that of v1. It may be that someone has
changed something on my host.., but it does not affect the display of
the optimization effect.)
In test2, we keep the number of the device the same as test1, reduce the
number of queues per device:
Here are the test2 results:
test info:
- Host
- Intel(R) Xeon(R) Platinum 8260 CPU
- NVIDIA Mellanox ConnectX-5
- VM
- 32 CPUs 128GB RAM VM
- 8 1-queue vhost-net device
- 16 1-queue vhost-user-blk device.
time of loading non-iterable vmstate downtime
before about 90 ms about 250 ms
after about 25 ms about 160 ms
In test3, we keep the number of queues per device the same as test1, reduce
the number of devices:
Here are the test3 results:
test info:
- Host
- Intel(R) Xeon(R) Platinum 8260 CPU
- NVIDIA Mellanox ConnectX-5
- VM
- 32 CPUs 128GB RAM VM
- 1 16-queue vhost-net device
- 1 4-queue vhost-user-blk device.
time of loading non-iterable vmstate downtime
before about 20 ms about 70 ms
after about 11 ms about 60 ms
As we can see from the test results above, both the number of queues and
the number of devices have a great impact on the time of loading non-iterable
vmstate. The growth of the number of devices and queues will lead to more
mr commits, and the time consumption caused by the flatview reconstruction
will also increase.
Please review, Chuang.
[v3]
- move virtio_load_check_delay() from virtio_memory_listener_commit() to
virtio_vmstate_change().
- add delay_check flag to VirtIODevice to make sure virtio_load_check_delay()
will be called when delay_check is true.
[v2]
- rebase to latest upstream.
- add sanity check to address_space_to_flatview().
- postpone the init of the vring cache until migration's loading completes.
[v1]
The duration of loading non-iterable vmstate accounts for a significant
portion of downtime (starting with the timestamp of source qemu stop and
ending with the timestamp of target qemu start). Most of the time is spent
committing memory region changes repeatedly.
This patch packs all the changes to memory region during the period of
loading non-iterable vmstate in a single memory transaction. With the
increase of devices, this patch will greatly improve the performance.
Here are the test results:
test vm info:
- 32 CPUs 128GB RAM
- 8 16-queue vhost-net device
- 16 4-queue vhost-user-blk device.
time of loading non-iterable vmstate
before about 210 ms
after about 40 ms
