From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Subject: Re: [PATCH] lib: change rte_ring dequeue to guarantee
 ordering before tail update
Date: Sat, 23 Jul 2016 15:06:22 +0530
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Cc: Juhamatti Kuusisaari <juhamatti.kuusisaari@coriant.com>, "dev@dpdk.org"
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To: Thomas Monjalon <thomas.monjalon@6wind.com>
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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.