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From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Ruifeng Wang <ruifeng.wang@arm.com>, <dev@dpdk.org>
Cc: <beilei.xing@intel.com>, <qi.z.zhang@intel.com>,
	<bruce.richardson@intel.com>, <jerinj@marvell.com>,
	<hemant.agrawal@nxp.com>,  <drc@linux.vnet.ibm.com>,
	<honnappa.nagarahalli@arm.com>, <stable@dpdk.org>, <nd@arm.com>
Subject: Re: [dpdk-stable] [PATCH v2 2/2] net/i40e: fix risk in Rx descriptor read in scalar path
Date: Wed, 29 Sep 2021 16:05:26 +0100
Message-ID: <bed992ff-3bd1-a831-e53e-77120f421ec0@intel.com> (raw)
In-Reply-To: <20210915083339.2424369-3-ruifeng.wang@arm.com>

On 9/15/2021 9:33 AM, Ruifeng Wang wrote:
> Rx descriptor is 16B/32B in size. If the DD bit is set, it indicates
> that the rest of the descriptor words have valid values. Hence, the
> word containing DD bit must be read first before reading the rest of
> the descriptor words.
> 
> Since the entire descriptor is not read atomically, on relaxed memory
> ordered systems like Aarch64, read of the word containing DD field
> could be reordered after read of other words.
> 
> Read barrier is inserted between read of the word with DD field
> and read of other words. The barrier ensures that the fetched data
> is correct.
> 
> Testpmd single core test showed no performance drop on x86 or N1SDP.
> On ThunderX2, 22% performance regression was observed.
> 

Is 22% performance drop value correct? That is a big drop, is it acceptable?

Is this performance drop valid for all Arm scalar datapath, or is it specific to
ThunderX2?

> Fixes: 7b0cf70135d1 ("net/i40e: support ARM platform")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>


  reply	other threads:[~2021-09-29 15:06 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-06  3:31 [dpdk-stable] [PATCH 0/2] i40e Rx descriptor loads ordering Ruifeng Wang
2021-09-06  3:32 ` [dpdk-stable] [PATCH 1/2] net/i40e: fix risk in Rx descriptor read in NEON vector path Ruifeng Wang
2021-09-14 18:33   ` Honnappa Nagarahalli
2021-09-15  8:42     ` Ruifeng Wang
2021-09-06  3:32 ` [dpdk-stable] [PATCH 2/2] net/i40e: fix risk in Rx descriptor read in scalar path Ruifeng Wang
2021-09-14 18:06   ` Honnappa Nagarahalli
2021-09-15  8:33 ` [dpdk-stable] [PATCH v2 0/2] i40e Rx descriptor loads ordering Ruifeng Wang
2021-09-15  8:33   ` [dpdk-stable] [PATCH v2 1/2] net/i40e: fix risk in Rx descriptor read in NEON vector path Ruifeng Wang
2021-09-15  8:33   ` [dpdk-stable] [PATCH v2 2/2] net/i40e: fix risk in Rx descriptor read in scalar path Ruifeng Wang
2021-09-29 15:05     ` Ferruh Yigit [this message]
2021-09-29 15:29       ` Honnappa Nagarahalli
2021-10-11 16:26         ` Ferruh Yigit
2021-10-19 11:14           ` Zhang, Qi Z
2021-11-05  6:57             ` Ruifeng Wang
2021-11-11 10:27               ` Ruifeng Wang
2021-11-11 12:27     ` Zhang, Qi Z
2021-09-24 11:08   ` [dpdk-stable] [PATCH v2 0/2] i40e Rx descriptor loads ordering Zhang, Qi Z

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