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Re: [Qemu-devel] [PATCH v4 30/32] migration: delay the postcopy-active s
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v4 30/32] migration: delay the postcopy-active state switch |
Date: |
Fri, 1 Dec 2017 12:34:32 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
* Peter Xu (address@hidden) wrote:
> Switch the state until we try to start the VM on destination side. The
> problem is that without doing this we may have a very small window that
> we'll be in such a state:
>
> - dst VM is in postcopy-active state,
> - main thread is handling MIG_CMD_PACKAGED message, which loads all the
> device states,
> - ram load thread is reading memory data from source.
>
> Then if we failed at this point when reading the migration stream we'll
> also switch to postcopy-paused state, but that is not what we want. If
> device states failed to load, we should fail the migration directly
> instead of pause.
>
> Postponing the state switch to the point when we have already loaded the
> devices' states and been ready to start running destination VM.
>
> Signed-off-by: Peter Xu <address@hidden>
If it's the only way, then this is OK; but I'd prefer you use a separate
flag somewhere to let you know this, because this means that
POSTCOPY_ACTIVE on the destination happens at a different point that it
does on the source (and changing it on the source I think will break
lots of things).
Can't you use the PostcopyState value and check if it's in
POSTCOPY_INCOMING_RUNNING?
Dave
> ---
> migration/savevm.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/migration/savevm.c b/migration/savevm.c
> index bc87b0e5b1..3bc792e320 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1584,8 +1584,6 @@ static void *postcopy_ram_listen_thread(void *opaque)
> QEMUFile *f = mis->from_src_file;
> int load_res;
>
> - migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
> - MIGRATION_STATUS_POSTCOPY_ACTIVE);
> qemu_sem_post(&mis->listen_thread_sem);
> trace_postcopy_ram_listen_thread_start();
>
> @@ -1748,6 +1746,14 @@ static int
> loadvm_postcopy_handle_run(MigrationIncomingState *mis)
> return -1;
> }
>
> + /*
> + * Declare that we are in postcopy now. We should already have
> + * all the device states loaded ready when reach here, and also
> + * the ram load thread running.
> + */
> + migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
> + MIGRATION_STATUS_POSTCOPY_ACTIVE);
> +
> data = g_new(HandleRunBhData, 1);
> data->bh = qemu_bh_new(loadvm_postcopy_handle_run_bh, data);
> qemu_bh_schedule(data->bh);
> --
> 2.13.6
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH v4 30/32] migration: delay the postcopy-active state switch,
Dr. David Alan Gilbert <=