Docker manifest push is slow can not operate in parallel

Description

The docker manifest push only deal with the metadata, but it is too slow.

In my server, this cost for about 30s to push the manifest which contain a X86 arch and an ARM arch.

and when I push three push manifest in parallel, it cost about 2min. not ~30s as expected.

Reproduce

docker manifest create --insecure harbor.xxx.local/x:v1 harbor.xxx.local/x_x86:v1  harbor.xxx.local/x_armv8:v1 
docker manifest push --insecure harbor.xxx.local/x:v1 

Expected behavior

expect the push can run in parallel

docker version

Client:
 Cloud integration: v1.0.28
 Version:           20.10.17
 API version:       1.41
 Go version:        go1.17.11
 Git commit:        100c701
 Built:             Mon Jun  6 23:04:45 2022
 OS/Arch:           darwin/amd64
 Context:           default
 Experimental:      true

Server: Docker Desktop 4.11.1 (84025)
 Engine:
  Version:          20.10.17
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.17.11
  Git commit:       a89b842
  Built:            Mon Jun  6 23:01:23 2022
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.6
  GitCommit:        10c12954828e7c7c9b6e0ea9b0c02b01407d3ae1
 runc:
  Version:          1.1.2
  GitCommit:        v1.1.2-0-ga916309
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.8.2)
  compose: Docker Compose (Docker Inc., v2.7.0)
  extension: Manages Docker extensions (Docker Inc., v0.2.8)
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc., 0.6.0)
  scan: Docker Scan (Docker Inc., v0.17.0)

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 0
 Server Version: 20.10.17
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 10c12954828e7c7c9b6e0ea9b0c02b01407d3ae1
 runc version: v1.1.2-0-ga916309
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.10.104-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 6
 Total Memory: 5.805GiB
 Name: docker-desktop
 ID: 2VO2:ARRA:QFIB:UJQJ:ESEG:3YTI:WLMF:YW3C:Q2ZA:M7RN:LU2Q:D6LG
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  harbor.xxx.local
  hubproxy.docker.internal:5000
  registry.xxx.local
  127.0.0.0/8
 Registry Mirrors:
  http://hub-mirror.c.163.com/
  https://reg-mirror.qiniu.com/
 Live Restore Enabled: false

Additional Info

No response

Start by reproducing the documented docker manifest create and docker manifest push commands with one manifest and then three concurrent pushes. Trace the manifest-push entry point to identify where operations are serialized; done means independent pushes proceed concurrently without the reported roughly two-minute total delay.