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From: | Daniel Henrique Barboza |
Subject: | Re: [Qemu-devel] [Qemu-ppc] [PATCH 0/4] spapr: disable hotplugging without OS |
Date: | Tue, 23 May 2017 14:52:54 -0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
Hi Laurent,This is an interesting patch series. I've been working in the last weeks in the DRC migration, mainly to solve the problem in which a hot CPU unplug will not succeed after a migration if the CPU was hotplugged in the source. The problem happened when migrating with virsh because Libvirt hotplugs the CPU in both source and target, and the DRC state of the hotplugged after the migration is inconsistent. This series solves the issue by preventing it from happening in the first place. Of course that migrating DRC states has other uses (pending unplug operations during a migration, for example) so both patch
series can coexist.One possible issue I see with this series is that it breaks Libvirt migration entirely if a CPU/mem hotplug happens in the target. With your series applied the migration
fails before start with:# ./virsh -c 'qemu:///system' migrate --live --domain dhb_ub1704_nfs --desturi qemu+ssh://target_ip/system --timeout 60 --verbose error: internal error: unable to execute QEMU command 'device_add': CPU hotplug not supported without OS
Note that I say "possible issue" because, although I believe we do not want to break Libvirt if possible, I also believe that we need to think about what makes sense in QEMU first.
Thanks, Daniel On 05/23/2017 08:18 AM, Laurent Vivier wrote:
If the OS is not started, QEMU sends an event to the OS that is lost and cannot be recovered. An unplug is not able to restore QEMU in a coherent state. So, while the OS is not started, disable CPU and memory hotplug. We use option vector 6 to know if the OS is started This series moves error checking for memory hotplug in a pre_plug function, and introduces the option vector 6 management. It also revert previous fix which was not really fixing the hotplug problem when the OS is not running. Laurent Vivier (4): spapr: add pre_plug function for memory spapr: add option vector 6 spapr: disable hotplugging without OS Revert "spapr: fix memory hot-unplugging" hw/ppc/spapr.c | 103 ++++++++++++++++++++++++++++++++++++-------- hw/ppc/spapr_drc.c | 20 ++------- hw/ppc/spapr_hcall.c | 5 ++- hw/ppc/spapr_ovec.c | 8 ++++ include/hw/ppc/spapr.h | 2 + include/hw/ppc/spapr_drc.h | 1 - include/hw/ppc/spapr_ovec.h | 7 +++ 7 files changed, 109 insertions(+), 37 deletions(-)
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