Re: [Qemu-devel] [PATCH v9 09/10] Add set_cachesize command

[Juan Quintela]

Orit Wasserman <address@hidden> wrote:
> Change XBZRLE cache size in bytes (the size should be a power of 2).
> If XBZRLE cache size is too small there will be many cache miss.

> +        .name       = "migrate_set_cachesize",
> +        .args_type  = "value:o",

This mean that we can assign values like 256M, right?  i.e. no way to
pass negative values?
> index 7578163..071a1b9 100644
> --- a/migration.c
> +++ b/migration.c
> @@ -167,7 +167,7 @@ MigrationCapList *qmp_query_migration_caps(Error **errp)
>      MigrationCapList *caps_list = g_malloc0(sizeof(*caps_list));
>  
>      caps_list->value = g_malloc(sizeof(*caps_list->value));
> -    caps_list->value->name = g_strdup("uleb");
> +    caps_list->value->name = g_strdup("xbzrle");
>      caps_list->next = NULL;
>  

Shouldn't this go in the previous patche?

> +void qmp_migrate_set_cachesize(int64_t value, Error **errp)
> +{
> +    MigrationState *s;
> +
> +    /* Check for truncation */
> +    if (value != (size_t)value) {
> +        error_set(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
> +                  "exceeding address space");
> +        return;
> +    }
> +
> +    /* power of 2 */
> +    if (value != 1 && (value & (value - 1))) {
> +        error_set(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
> +                  "needs to be power of 2");
> +        return;
> +    }

Don't we have a function to calculate if a value is a power of 2 in
qemu?  I guess we need one _now_.

> +
> +    value = MIN(UINT64_MAX, value);
> +    if (value ==  migrate_cache_size) {
> +        return;
> +    }
> +
> +    migrate_cache_size =  value;

Can't we just remove the migrate_cache_size as a new field of
migration_state.  bandwidth_limit is the example on how to do it.

Thanks, Juan.