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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Kunkun Jiang <jiangkunkun@huawei.com>
Cc: "Juan Quintela" <quintela@redhat.com>,
	"David Edmondson" <dme@dme.org>,
	"open list:All patches CC here" <qemu-devel@nongnu.org>,
	"Peter Xu" <peterx@redhat.com>, "Cédric Le Goater" <clg@kaod.org>,
	"Alexey Romko" <nevilad@yahoo.com>,
	"Zenghui Yu" <yuzenghui@huawei.com>,
	wanghaibin.wang@huawei.com, "Keqian Zhu" <zhukeqian1@huawei.com>,
	"Andrey Gruzdev" <andrey.gruzdev@virtuozzo.com>
Subject: Re: [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting
Date: Wed, 17 Mar 2021 12:05:27 +0000	[thread overview]
Message-ID: <YFHwh7bIr3Mua6Pe@work-vm> (raw)
In-Reply-To: <cbbe92e2-4ebf-476a-3733-8e1c7893702e@huawei.com>

* Kunkun Jiang (jiangkunkun@huawei.com) wrote:
> Hi  Peter,
> 
> On 2021/3/17 5:39, Peter Xu wrote:
> > 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! :)
> > 
> You are very serious and meticulous. I like your character very much.😉
> This patch was used to reviewed by David. So, I want to know what
> his opinion is.
> 
> @David
> Hi David, what is your opinion on this patch?

Yes, I think this is OK;
  a) The qemu_file_rate_limit in the loop in ram_save_iterate still
     gets called, so that covers the 'pagesize_bits > 1' part of the if
  b) As soon as we send any part of the hugepage the 'tmppages > 0'
     triggers and we get the check back again.

So I guess this mostly helps the case where we have big huge pages
which are mostly not-dirty, and we spend a lot of time in
ram_save_host_page searching for the target page to send.



Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> Thanks,
> Kunkun Jiang
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK



  parent reply	other threads:[~2021-03-17 12:07 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-16 12:57 [PATCH v4 0/2] Some modification about ram_save_host_page() Kunkun Jiang
2021-03-16 12:57 ` [PATCH v4 1/2] migration/ram: Reduce unnecessary rate limiting Kunkun Jiang
2021-03-16 21:39   ` Peter Xu
2021-03-17  1:37     ` Kunkun Jiang
2021-03-17 10:43       ` David Edmondson
2021-03-17 12:05       ` Dr. David Alan Gilbert [this message]
2021-03-16 12:57 ` [PATCH v4 2/2] migration/ram: Optimize ram_save_host_page() Kunkun Jiang
2021-03-16 21:39   ` Peter Xu
2021-04-06 13:19 ` [PATCH v4 0/2] Some modification about ram_save_host_page() Kunkun Jiang
2021-04-06 17:14   ` Dr. David Alan Gilbert
2021-04-07  9:32     ` Kunkun Jiang
2021-05-11  9:17 ` Dr. David Alan Gilbert

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