Re: [Qemu-devel] [RFC v2 0/6] QEMU shared-memory backend

[Markus Armbruster]

Copying Paolo, author of memory-backend-file.

Baptiste Reynal <address@hidden> writes:

> A new memory backend, the shared memory backend, based on
> the file memory backend.
>
> This new backend allows a master QEMU instance to share a part of
> his main memory whith a slave QEMU instance. It is then possible to load
> a firmware on this memory and trigger the slave boot using a SDM
> signal.

Can you explain why that's useful in a bit more detail?

> Such new backend enables, on a master side, to allocate the whole
> memory as shareable (e.g. /dev/shm, or hugetlbfs).

memory-backend-file can do that already.  What exactly does
memory-backend-shared add to it?

> On the slave side it enables the startup of QEMU without any main memory
> allocated. Then the slave goes in a waiting state, the same used in the
> case of an incoming migration, and the file descriptor of the shared
> memory is sent by the master over a socket.
> The waiting state ends when the master sends to the slave a signal
> with size and offset to mmap and use as memory as payload.
>
> You can test those patches using modules and test application available
> on https://git.virtualopensystems.com/dev/qemu-het-tools.
> - SDM Platform module on branch sdm_test_mod_v1
> - Test application on branch sdm_test_app
> - Slave files on branch demo_slaves_sdm
>
>  QEMU code is avalaible here https://git.virtualopensystems.com/dev/qemu on 
> branch rfc_v2.
>
> Run QEMU master instance:
> ./qemu-system-arm -nographic \
>         -kernel zImage \
>         -M virt -m 1G \
>         -initrd busybox.cpio \
>         -object multi-socket-backend,id=sock,path=sock,listen \
>         -object 
> memory-backend-shared,id=mem,size=1G,mem-path=/dev/hugepages,socket=sock,master
>  \
>         -object sdm-signal-shboot,id=boot,shm=mem \
>         -object sdm-communication-socket,id=scomm,socket=sock \
>         -device 
> virtio-sdm-device,comm=scomm,master,num-slaves=1,len-signals=1,signals[0]=boot
>  \
>         -append "mem=512M memmap=512M$0x60000000" \
>         -numa node,memdev=mem -m 1G
>
> Run QEMU slave instance:
> ./qemu-system-arm -nographic \
>         -kernel zImage \
>         -M virt -m 1G \
>         -initrd busybox.cpio \
>         -object multi-socket-backend,id=sock,path=sock \
>         -object memory-backend-shared,id=mem,size=512M,socket=sock \
>         -object sdm-signal-shboot,id=boot,shm=mem \
>         -object sdm-communication-socket,id=scomm,socket=sock \
>         -device sdm-platform,comm=scomm,len-signals=1,signals[0]="boot" \
>         -incoming "shared:mem" \
>         -numa node,memdev=mem -m 512M
>
> On the master, load the SDM module (insmod sdm_test_mod_v1) and trigger the 
> boot with
> the following command:
> ./sdm-test -b 0 1 zImage slave.dtb
>
> zImage and slave.dtb are available on branch demo_slaves_sdm.
>
> This patch serie is a follow-up to "[RFC PATCH 0/8] Towards an Heterogeneous 
> QEMU":
> https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg00171.html
>
> This patch serie depends on:
> - [RFC v2 0/6] SDM Interface
> - [RFC v2 1/1] backend: multi-client-socket
>
> This work has been sponsored by Huawei Technologies Duesseldorf GmbH.
>
> Baptiste Reynal (3):
>   backend: shared memory backend
>   migration: add shared migration type
>   hw/misc: sdm signal shboot
>
> Christian Pinto (3):
>   qemu: slave machine flag
>   hw/arm: boot
>   qemu: numa
>
>  backends/Makefile.objs              |   2 +-
>  backends/hostmem-shared.c           | 198 
> ++++++++++++++++++++++++++++++++++++
>  hw/arm/boot.c                       |  13 +++
>  hw/core/machine.c                   |  27 +++++
>  hw/misc/Makefile.objs               |   1 +
>  hw/misc/sdm-signal-shboot.c         |  62 +++++++++++
>  include/hw/boards.h                 |   2 +
>  include/hw/misc/sdm-signal-shboot.h |  38 +++++++
>  include/migration/migration.h       |   2 +
>  include/sysemu/hostmem-shared.h     |  66 ++++++++++++
>  migration/Makefile.objs             |   2 +-
>  migration/migration.c               |   2 +
>  migration/shared.c                  |  33 ++++++
>  numa.c                              |  17 +++-
>  qemu-options.hx                     |   5 +-
>  util/qemu-config.c                  |   5 +
>  16 files changed, 471 insertions(+), 4 deletions(-)
>  create mode 100644 backends/hostmem-shared.c
>  create mode 100644 hw/misc/sdm-signal-shboot.c
>  create mode 100644 include/hw/misc/sdm-signal-shboot.h
>  create mode 100644 include/sysemu/hostmem-shared.h
>  create mode 100644 migration/shared.c