From: Jerin Jacob <jerin.jacob@caviumnetworks.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: Juhamatti Kuusisaari <juhamatti.kuusisaari@coriant.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Subject: Re: [dpdk-dev] [PATCH] lib: change rte_ring dequeue to guarantee ordering before tail update
Date: Sat, 23 Jul 2016 15:06:22 +0530 [thread overview]
Message-ID: <20160723093621.GA18376@localhost.localdomain> (raw)
In-Reply-To: <CA+PrjLGmaYppXVLR190Qn3B-JQVsvY1ZHGQexvKXs0_MOt8FmA@mail.gmail.com>
On Sat, Jul 23, 2016 at 11:02:33AM +0200, Thomas Monjalon wrote:
> 2016-07-23 8:05 GMT+02:00 Jerin Jacob <jerin.jacob@caviumnetworks.com>:
> > On Thu, Jul 21, 2016 at 11:26:50PM +0200, Thomas Monjalon wrote:
> >> > > Consumer queue dequeuing must be guaranteed to be done fully before the tail is updated. This is not guaranteed with a read barrier,
> >> > > changed to a write barrier just before tail update which in practice guarantees correct order of reads and writes.
> >> > >
> >> > > Signed-off-by: Juhamatti Kuusisaari <juhamatti.kuusisaari@coriant.com>
> >> >
> >> > Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> >>
> >> Applied, thanks
> >
> > There was ongoing discussion on this
> > http://dpdk.org/ml/archives/dev/2016-July/044168.html
>
> Sorry Jerin, I forgot this email.
> The problem is that nobody replied to your email and you did not nack
> the v2 of this patch.
>
> > This change may not be required as it has the performance impact.
>
> We need to clearly understand what is the performance impact
> (numbers and use cases) on one hand, and is there a real bug fixed
> by this patch on the other hand?
IHMO, there is no real bug here. rte_smb_rmb() provides the LOAD-STORE
barrier to make sure tail pointer WRITE happens only after prior LOADS.
Thoughts?
>
> Please guys make things clear and we'll revert if needed.
next prev parent reply other threads:[~2016-07-23 9:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-15 4:39 Juhamatti Kuusisaari
2016-07-15 12:22 ` Ananyev, Konstantin
2016-07-21 21:26 ` Thomas Monjalon
2016-07-23 6:05 ` Jerin Jacob
2016-07-23 9:02 ` Thomas Monjalon
2016-07-23 9:36 ` Jerin Jacob [this message]
2016-07-23 10:14 ` Ananyev, Konstantin
2016-07-23 10:38 ` Jerin Jacob
2016-07-23 11:15 ` Ananyev, Konstantin
2016-07-23 11:49 ` Jerin Jacob
2016-07-23 12:32 ` Ananyev, Konstantin
2016-07-23 12:35 ` Jerin Jacob
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