migration: Create the postcopy preempt channel asynchronously
This patch allows the postcopy preempt channel to be created asynchronously. The benefit is that when the connection is slow, we won't take the BQL (and potentially block all things like QMP) for a long time without releasing. A function postcopy_preempt_wait_channel() is introduced, allowing the migration thread to be able to wait on the channel creation. The channel is always created by the main thread, in which we'll kick a new semaphore to tell the migration thread that the channel has created. We'll need to wait for the new channel in two places: (1) when there's a new postcopy migration that is starting, or (2) when there's a postcopy migration to resume. For the start of migration, we don't need to wait for this channel until when we want to start postcopy, aka, postcopy_start(). We'll fail the migration if we found that the channel creation failed (which should probably not happen at all in 99% of the cases, because the main channel is using the same network topology). For a postcopy recovery, we'll need to wait in postcopy_pause(). In that case if the channel creation failed, we can't fail the migration or we'll crash the VM, instead we keep in PAUSED state, waiting for yet another recovery. Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: NManish Mishra <manish.mishra@nutanix.com> Signed-off-by: NPeter Xu <peterx@redhat.com> Message-Id: <20220707185509.27311-1-peterx@redhat.com> Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Showing
想要评论请 注册 或 登录