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From: "Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Cc: nd <nd@arm.com>, "thomas@monjalon.net" <thomas@monjalon.net>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	"pbhagavatula@marvell.com" <pbhagavatula@marvell.com>,
	"qi.z.zhang@intel.com" <qi.z.zhang@intel.com>,
	"bruce.richardson@intel.com" <bruce.richardson@intel.com>,
	"stable@dpdk.org" <stable@dpdk.org>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH 1/2] net/i40e: desc loading is unnecessarily ordered for aarch64
Date: Fri, 30 Aug 2019 08:33:47 +0000	[thread overview]
Message-ID: <VI1PR08MB53769E184436606E8DC4DDB28FBD0@VI1PR08MB5376.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <VE1PR08MB5149D7E5217A0E7F09358A4798A30@VE1PR08MB5149.eurprd08.prod.outlook.com>

Hi Honnappa,

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Thursday, August 29, 2019 6:10 AM
> To: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>;
> dev@dpdk.org
> Cc: nd <nd@arm.com>; thomas@monjalon.net; jerinj@marvell.com;
> pbhagavatula@marvell.com; qi.z.zhang@intel.com;
> bruce.richardson@intel.com; stable@dpdk.org; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH 1/2] net/i40e: desc loading is unnecessarily ordered for
> aarch64
> 
> Thanks Gavin, few comments are inline
> 
> > -----Original Message-----
> > From: Gavin Hu <gavin.hu@arm.com>
> > Sent: Tuesday, August 13, 2019 5:44 AM
> > To: dev@dpdk.org
> > Cc: nd <nd@arm.com>; thomas@monjalon.net; jerinj@marvell.com;
> > pbhagavatula@marvell.com; Honnappa Nagarahalli
> > <Honnappa.Nagarahalli@arm.com>; qi.z.zhang@intel.com;
> > bruce.richardson@intel.com; stable@dpdk.org
> > Subject: [PATCH 1/2] net/i40e: desc loading is unnecessarily ordered for
> > aarch64
> >
> > For x86, the descriptors needs to be loaded in order, so in between two
> > descriptors loading, there is a compiler barrier in place.
> IMO, we can skip the above as this change applies to Arm platforms. Instead,
> capture this in the code in comments to explain why the ordering of the
> loads is not required. This will help others reading the code.

As the line of code was removed, there is no suitable place to add a comment.
Instead adding it in the commit log makes the story complete and easy to understand. 

> [1] For aarch64, a
> > patch [2] is in place to survive with discontinuous DD bits, the barriers can
> be
> > removed to take full advantage of out-of-order execution.
> >
> > 50% performance gain in the RFC2544 NDR test was measured on
> ThunderX2.
> > 12.50% performan gain in the RFC2544 NDR test was measured on
> Ampere
> > eMAG80 platform.
> >
> > [1]
> >
> http://inbox.dpdk.org/users/039ED4275CED7440929022BC67E7061153D71
> > 548@
> > SHSMSX105.ccr.corp.intel.com/
> > [2] https://mails.dpdk.org/archives/stable/2017-October/003324.html
> >
> > Fixes: ae0eb310f253 ("net/i40e: implement vector PMD for ARM")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > Reviewed-by: Steve Capper <steve.capper@arm.com>
> > ---
> >  drivers/net/i40e/i40e_rxtx_vec_neon.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/net/i40e/i40e_rxtx_vec_neon.c
> > b/drivers/net/i40e/i40e_rxtx_vec_neon.c
> > index 83572ef..5555e9b 100644
> > --- a/drivers/net/i40e/i40e_rxtx_vec_neon.c
> > +++ b/drivers/net/i40e/i40e_rxtx_vec_neon.c
> > @@ -285,7 +285,6 @@ _recv_raw_pkts_vec(struct i40e_rx_queue *rxq,
> > struct rte_mbuf **rx_pkts,
> >  		/* Read desc statuses backwards to avoid race condition */
> >  		/* A.1 load 4 pkts desc */
> >  		descs[3] =  vld1q_u64((uint64_t *)(rxdp + 3));
> > -		rte_rmb();
> >
> >  		/* B.2 copy 2 mbuf point into rx_pkts  */
> >  		vst1q_u64((uint64_t *)&rx_pkts[pos], mbp1);
> > --
> > 2.7.4

  reply	other threads:[~2019-08-30  8:34 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 10:43 [dpdk-dev] [PATCH 0/2] i40e neon vPMD optiomization " Gavin Hu
2019-08-13 10:43 ` [dpdk-dev] [PATCH 1/2] net/i40e: desc loading is unnecessarily ordered " Gavin Hu
2019-08-28 22:09   ` Honnappa Nagarahalli
2019-08-30  8:33     ` Gavin Hu (Arm Technology China) [this message]
2019-08-13 10:43 ` [dpdk-dev] [PATCH 2/2] net/i40e: remove compiler barrier " Gavin Hu
2019-08-28 22:48   ` Honnappa Nagarahalli
2019-08-30  8:51     ` Gavin Hu (Arm Technology China)
2019-09-04  7:49 ` [dpdk-dev] [PATCH 0/2] i40e neon vPMD optiomization " Ferruh Yigit

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