Re: [PATCH RESEND v6 0/5] migration: reduce time of loading non-iterable vmstate

[Peter Xu]

Hi, Chuang,

On Fri, Mar 03, 2023 at 06:56:50PM +0800, Chuang Xu wrote:
> Sorry to forget to update the test results in the last patch of v6.
> 
> In this version:
> 
> - add peter's patch.
> - split mr_do_commit() from mr_commit().
> - adjust the sanity check in address_space_to_flatview().
> - rebase to latest upstream.
> - replace 8260 with 8362 as testing host.
> - update the latest test results.
> 
> Here I list some cases which will trigger do_commit() in 
> address_space_to_flatview():
> 
> 1.virtio_load->virtio_init_region_cache
> 2.virtio_load->virtio_set_features_nocheck

What is this one specifically?  I failed to see quickly why this needs to
reference the flatview.

> 3.vapic_post_load

Same confusion to this one..

> 4.tcg_commit

This is not enabled if kvm is on, right?

> 5.ahci_state_post_load
> 
> During my test, virtio_init_region_cache() will frequently trigger
> do_commit() in address_space_to_flatview(), which will reduce the
> optimization  effect of v6 compared with v1.

IIU above 1 & 4 could leverage one address_space_to_flatview_rcu() which
can keep the old semantics of address_space_to_flatview() by just assert
rcu read lock and do qatomic_rcu_read() (e.g., tcg_commit() will run again
at last stage of vm load).  Not sure how much it'll help.

You may also want to have a look at the other patch to optimize ioeventfd
commit here; I think that'll also speed up vm load but not sure how much
your series can further do upon:

https://lore.kernel.org/all/20230228142514.2582-1-longpeng2@huawei.com/

Thanks,

-- 
Peter Xu