From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Juan Quintela <quintela@redhat.com>
Cc: qemu-devel@nongnu.org, peterx@redhat.com, LMa@suse.com
Subject: Re: [PATCH] migration: Rate limit inside host pages
Date: Thu, 5 Dec 2019 14:30:37 +0000 [thread overview]
Message-ID: <20191205143037.GI2824@work-vm> (raw)
In-Reply-To: <87o8wmkhd4.fsf@trasno.org>
* Juan Quintela (quintela@redhat.com) wrote:
> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> >
> > 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 <LMa@suse.com>
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
>
> Reviewed-by: Juan Quintela <quintela@redhat.com>
>
> 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
> pages.
Right.
> Not that it should be a big issue (performance wise).
> Have you done any meassuremnet?
I've just given it a quick run; it still seems to be hitting ~9.5Gbps on
my 10Gbps interface; so it doesn't seem to be the limit on that.
Dave
>
>
> Later, Juan.
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
next prev parent reply other threads:[~2019-12-05 14:33 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-05 10:29 [PATCH] migration: Rate limit inside host pages Dr. David Alan Gilbert (git)
2019-12-05 13:54 ` Juan Quintela
2019-12-05 14:30 ` Dr. David Alan Gilbert [this message]
2019-12-05 13:55 ` Peter Xu
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