Re: [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting

[Peter Xu]

On Tue, Mar 16, 2021 at 08:57:15PM +0800, Kunkun Jiang wrote:
> When the host page is a huge page and something is sent in the
> current iteration, migration_rate_limit() should be executed.
> If not, it can be omitted.
> 
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> Reviewed-by: David Edmondson <david.edmondson@oracle.com>
> ---
>  migration/ram.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 72143da0ac..3eb5b0d7a7 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2015,8 +2015,13 @@ static int ram_save_host_page(RAMState *rs, 
> PageSearchStatus *pss,
>  
>          pages += tmppages;
>          pss->page++;
> -        /* Allow rate limiting to happen in the middle of huge pages */
> -        migration_rate_limit();
> +        /*
> +         * Allow rate limiting to happen in the middle of huge pages if
> +         * something is sent in the current iteration.
> +         */
> +        if (pagesize_bits > 1 && tmppages > 0) {
> +            migration_rate_limit();
> +        }

Sorry I'm still not a fan of this - I'd even prefer calling that once more just
to make sure it won't be forgotten to be called..  Not to say it's merely a 
noop.

I'll leave this to Dave..  Maybe I'm too harsh! :)

-- 
Peter Xu