From: "Zhang, Qi Z" <firstname.lastname@example.org>
To: "Yigit, Ferruh" <email@example.com>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
Ruifeng Wang <Ruifeng.Wang@arm.com>,
"Min Hu (Connor)" <firstname.lastname@example.org>,
"Yisen Zhuang" <email@example.com>,
Lijun Ou <firstname.lastname@example.org>
Cc: "Xing, Beilei" <email@example.com>,
"Richardson, Bruce" <firstname.lastname@example.org>,
"email@example.com" <firstname.lastname@example.org>, nd <email@example.com>,
Subject: Re: [dpdk-dev] [dpdk-stable] [PATCH v2 2/2] net/i40e: fix risk in Rx descriptor read in scalar path
Date: Tue, 19 Oct 2021 11:14:43 +0000 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
> -----Original Message-----
> From: Yigit, Ferruh <email@example.com>
> Sent: Tuesday, October 12, 2021 12:27 AM
> To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; firstname.lastname@example.org; Min Hu (Connor)
> <email@example.com>; Yisen Zhuang <firstname.lastname@example.org>; Lijun
> Ou <email@example.com>
> Cc: Xing, Beilei <firstname.lastname@example.org>; Zhang, Qi Z <email@example.com>;
> Richardson, Bruce <firstname.lastname@example.org>; email@example.com;
> firstname.lastname@example.org; email@example.com; firstname.lastname@example.org; nd
> <email@example.com>; firstname.lastname@example.org
> Subject: Re: [dpdk-stable] [PATCH v2 2/2] net/i40e: fix risk in Rx descriptor
> read in scalar path
> On 9/29/2021 4:29 PM, Honnappa Nagarahalli wrote:
> > <snip>
> >> 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?
> > Agree, it is a big drop. Fixing it will require using the barrier less frequently.
> For ex: read 4 descriptors (4 words containing the DD bits) before using the
> >> Is this performance drop valid for all Arm scalar datapath, or is it
> >> specific to ThunderX2?
> > This is specific to ThunderX2. N1 CPU does not see any impact. A72 is not
> tested. Considering that the ThunderXx line of CPUs are not in further
> development, and it is scalar path, I would not suggest to make further
> changes to the code.
> > It would be good to test this on Kunpeng servers and get some feedback.
> Hi Connor, Yisen, Lijun,
> Can you please check this patch? I don't know if you are using i40e nic on your
> platform but if you do can you please test it?
> Overall this patch cause a big performance drop on Arm for i40e, I just want to
> be sure this is not impacting any user negatively.
This patch has been dropped from dpdk-next-net-intel, as still waiting for your confirm.
Btw Patch 1/2 was still in dpdk-next-net-intel.
> >>> Fixes: 7b0cf70135d1 ("net/i40e: support ARM platform")
> >>> Cc: email@example.com
> >>> Signed-off-by: Ruifeng Wang <firstname.lastname@example.org>
> >>> Reviewed-by: Honnappa Nagarahalli <email@example.com>
next prev parent reply other threads:[~2021-10-19 11:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-06 3:31 [dpdk-dev] [PATCH 0/2] i40e Rx descriptor loads ordering Ruifeng Wang
2021-09-06 3:32 ` [dpdk-dev] [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-dev] [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-dev] [PATCH v2 0/2] i40e Rx descriptor loads ordering Ruifeng Wang
2021-09-15 8:33 ` [dpdk-dev] [PATCH v2 1/2] net/i40e: fix risk in Rx descriptor read in NEON vector path Ruifeng Wang
2021-09-15 8:33 ` [dpdk-dev] [PATCH v2 2/2] net/i40e: fix risk in Rx descriptor read in scalar path Ruifeng Wang
2021-09-29 15:05 ` [dpdk-dev] [dpdk-stable] " Ferruh Yigit
2021-09-29 15:29 ` Honnappa Nagarahalli
2021-10-11 16:26 ` Ferruh Yigit
2021-10-19 11:14 ` Zhang, Qi Z [this message]
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-dev] [PATCH v2 0/2] i40e Rx descriptor loads ordering Zhang, Qi Z
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