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Re: [PATCH] migration: Rate limit inside host pages

From: Juan Quintela
Subject: Re: [PATCH] migration: Rate limit inside host pages
Date: Thu, 05 Dec 2019 14:54:31 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)

"Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> When using hugepages, rate limiting is necessary within each huge
> page, since a 1G huge page can take a significant time to send, so
> you end up with bursty behaviour.
> Fixes: 4c011c37ecb3 ("postcopy: Send whole huge pages")
> Reported-by: Lin Ma <address@hidden>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---

Reviewed-by: Juan Quintela <address@hidden>

I can agree that rate limit needs to be done for huge pages.

> diff --git a/migration/ram.c b/migration/ram.c
> index a4ae3b3120..a9177c6a24 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2616,6 +2616,8 @@ 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();
>      } while ((pss->page & (pagesize_bits - 1)) &&
>               offset_in_ramblock(pss->block, pss->page << TARGET_PAGE_BITS));

But is doing the rate limit for each page, no?  Even when not using huge

Not that it should be a big issue (performance wise).
Have you done any meassuremnet?

Later, Juan.

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