Re: [Qemu-devel] [PATCH v5 3/5] migration: Dynamic cpu throttling for auto-converge

[Eric Blake <eblake@redhat.com>]

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On 09/01/2015 08:46 AM, Jason J. Herne wrote:
> Remove traditional auto-converge static 30ms throttling code and replace it
> with a dynamic throttling algorithm.
> 
> Additionally, be more aggressive when deciding when to start throttling.
> Previously we waited until four unproductive memory passes. Now we begin
> throttling after only two unproductive memory passes. Four seemed quite
> arbitrary and only waiting for two passes allows us to complete the migration
> faster.
> 
> Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
> Reviewed-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
> ---
>  arch_init.c           | 88 ++++++++++++++++++---------------------------------
>  migration/migration.c |  4 +++
>  2 files changed, 34 insertions(+), 58 deletions(-)

> +static void mig_throttle_guest_down(void)
> +{
> +    MigrationState *s = migrate_get_current();
> +    uint64_t pct_initial =
> +            s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INITIAL];
> +    uint64_t pct_icrement =
> +            s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT];
> +
> +    /* We have not started throttling yet. Let's start it. */
> +    if (!cpu_throttle_active()) {
> +        cpu_throttle_set(pct_initial);
> +    } else {
> +        /* Throttling already on, just increase the rate */
> +        cpu_throttle_set(cpu_throttle_get_percentage() + pct_icrement);

What happens if the addition results in a percentage larger than 99?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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