[dpdk-stable] patch 'vhost: avoid concurrency when logging dirty pages' has been queued to stable release 18.02.2

[Luca Boccassi]

On Mon, 2018-04-30 at 16:44 +0200, Maxime Coquelin wrote:
> Hi Luca,
> 
> Please don't backport this patch to -stable releases.
> It has already been reverted in upstream master, and a new patch is
> to
> be posted in the coming hours.
> 
> I already notified Yuanhan for the same for v17.11 LTS.
> 
> Thanks,
> Maxime

Ok, removed, thanks for the heads-up.

> On 04/30/2018 04:40 PM, luca.boccassi at gmail.com wrote:
> > Hi,
> > 
> > FYI, your patch has been queued to stable release 18.02.2
> > 
> > Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable
> > yet.
> > It will be pushed if I get no objections before 05/02/18. So please
> > shout if anyone has objections.
> > 
> > Thanks.
> > 
> > Luca Boccassi
> > 
> > ---
> >  From a5d642c446cc3a3be41694715d99f3e9f9ea44df Mon Sep 17 00:00:00
> > 2001
> > From: Maxime Coquelin <maxime.coquelin at redhat.com>
> > Date: Wed, 21 Mar 2018 16:44:13 +0100
> > Subject: [PATCH] vhost: avoid concurrency when logging dirty pages
> > 
> > [ upstream commit 394313fff39d0f994325c47f7eab39daf5dc9e11 ]
> > 
> > This patch aims at fixing a migration performance regression
> > faced since atomic operation is used to log pages as dirty when
> > doing live migration.
> > 
> > Instead of setting a single bit by doing an atomic read-modify-
> > write
> > operation to log a page as dirty, this patch write 0xFF to the
> > corresponding byte, and so logs 8 page as dirty.
> > 
> > The advantage is that it avoids concurrent atomic operations by
> > multiple PMD threads, the drawback is that some clean pages are
> > marked as dirty and so are transferred twice.
> > 
> > Fixes: 897f13a1f726 ("vhost: make page logging atomic")
> > 
> > Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
> > Reviewed-by: Jianfeng Tan <jianfeng.tan at intel.com>
> > ---
> >   lib/librte_vhost/vhost.h | 12 ++++--------
> >   1 file changed, 4 insertions(+), 8 deletions(-)
> > 
> > diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> > index bab0b456e..a4f23f714 100644
> > --- a/lib/librte_vhost/vhost.h
> > +++ b/lib/librte_vhost/vhost.h
> > @@ -247,18 +247,14 @@ struct virtio_net {
> >   #define VHOST_LOG_PAGE	4096
> >   
> >   /*
> > - * Atomically set a bit in memory.
> > + * Mark all pages belonging to the same dirty log bitmap byte
> > + * as dirty. The goal is to avoid concurrency between different
> > + * threads doing atomic read-modify-writes on the same byte.
> >    */
> > -static __rte_always_inline void
> > -vhost_set_bit(unsigned int nr, volatile uint8_t *addr)
> > -{
> > -	__sync_fetch_and_or_8(addr, (1U << nr));
> > -}
> > -
> >   static __rte_always_inline void
> >   vhost_log_page(uint8_t *log_base, uint64_t page)
> >   {
> > -	vhost_set_bit(page % 8, &log_base[page / 8]);
> > +	log_base[page / 8] = 0xff;
> >   }
> >   
> >   static __rte_always_inline void
> > 

-- 
Kind regards,
Luca Boccassi