RE: [PATCH 07/10] Disable auto-coverge before entering COLO mode.

["Rao, Lei" <lei.rao@intel.com>]

Sorry for the late reply due to CNY.
Auto-converge ensure that live migration can be completed smoothly when there are too many dirty pages.
COLO may encounter the same situation when rebuild a new secondary VM. 
So, I think it is necessary to enable COLO and auto-converge at the same time.

Thanks,
Lei.

-----Original Message-----
From: Lukas Straub <lukasstraub2@web.de> 
Sent: Sunday, February 14, 2021 6:52 PM
To: Rao, Lei <lei.rao@intel.com>
Cc: Zhang, Chen <chen.zhang@intel.com>; lizhijian@cn.fujitsu.com; jasowang@redhat.com; zhang.zhanghailiang@huawei.com; quintela@redhat.com; dgilbert@redhat.com; qemu-devel@nongnu.org
Subject: Re: [PATCH 07/10] Disable auto-coverge before entering COLO mode.

On Wed, 13 Jan 2021 10:46:32 +0800
leirao <lei.rao@intel.com> wrote:

> From: "Rao, Lei" <lei.rao@intel.com>
> 
> If we don't disable the feature of auto-converge for live migration 
> before entering COLO mode, it will continue to run with COLO running, 
> and eventually the system will hang due to the CPU throttle reaching 
> DEFAULT_MIGRATE_MAX_CPU_THROTTLE.
> 
> Signed-off-by: Lei Rao <lei.rao@intel.com>
> ---
>  migration/migration.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c index 
> 31417ce..6ab37e5 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1673,6 +1673,20 @@ void migrate_set_block_enabled(bool value, Error **errp)
>      qapi_free_MigrationCapabilityStatusList(cap);
>  }
>  
> +static void colo_auto_converge_enabled(bool value, Error **errp) {
> +    MigrationCapabilityStatusList *cap = NULL;
> +
> +    if (migrate_colo_enabled() && migrate_auto_converge()) {
> +        QAPI_LIST_PREPEND(cap,
> +                          migrate_cap_add(MIGRATION_CAPABILITY_AUTO_CONVERGE,
> +                                          value));
> +        qmp_migrate_set_capabilities(cap, errp);
> +        qapi_free_MigrationCapabilityStatusList(cap);
> +    }
> +    cpu_throttle_stop();
> +}
> +

I think it's better to error out in migration_prepare or migrate_caps_check if both colo and auto-converge is enabled.

>  static void migrate_set_block_incremental(MigrationState *s, bool 
> value)  {
>      s->parameters.block_incremental = value; @@ -3401,7 +3415,7 @@ 
> static MigIterateState migration_iteration_run(MigrationState *s)  
> static void migration_iteration_finish(MigrationState *s)  {
>      /* If we enabled cpu throttling for auto-converge, turn it off. */
> -    cpu_throttle_stop();
> +    colo_auto_converge_enabled(false, &error_abort);
>  
>      qemu_mutex_lock_iothread();
>      switch (s->state) {



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