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From: Thomas Monjalon <thomas@monjalon.net>
To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
Cc: "Burakov, Anatoly" <anatoly.burakov@intel.com>,
	David Marchand <david.marchand@redhat.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	John McNamara <john.mcnamara@intel.com>,
	Marko Kovacevic <marko.kovacevic@intel.com>,
	Igor Russkikh <igor.russkikh@aquantia.com>,
	Pavel Belous <pavel.belous@aquantia.com>,
	Ajit Khaparde <ajit.khaparde@broadcom.com>,
	Somnath Kotur <somnath.kotur@broadcom.com>,
	Wenzhuo Lu <wenzhuo.lu@intel.com>,
	John Daley <johndale@cisco.com>,
	Hyong Youb Kim <hyonkim@cisco.com>,
	Qi Zhang <qi.z.zhang@intel.com>,
	Xiao Wang <xiao.w.wang@intel.com>,
	Beilei Xing <beilei.xing@intel.com>,
	Jingjing Wu <jingjing.wu@intel.com>,
	Qiming Yang <qiming.yang@intel.com>,
	Konstantin Ananyev <konstantin.ananyev@intel.com>,
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	Shahaf Shuler <shahafs@mellanox.com>,
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	Viacheslav Ovsiienko <viacheslavo@mellanox.com>,
	Alejandro Lucero <alejandro.lucero@netronome.com>,
	Nithin Kumar Dabilpuram <ndabilpuram@marvell.com>,
	Kiran Kumar Kokkilagadda <kirankumark@marvell.com>,
	Rasesh Mody <rmody@marvell.com>,
	Shahed Shaikh <shshaikh@marvell.com>,
	Bruce Richardson <bruce.richardson@intel.com>,
	"alialnu@mellanox.com" <alialnu@mellanox.com>,
	"aconole@redhat.com" <aconole@redhat.com>
Subject: Re: [dpdk-dev] [PATCH 2/2] eal: fix IOVA mode selection as VA for pci drivers
Date: Mon, 15 Jul 2019 18:06:26 +0200
Message-ID: <1689145.QdohnT2lii@xps> (raw)
In-Reply-To: <BYAPR18MB2424274AE715A946EDF96629C8CF0@BYAPR18MB2424.namprd18.prod.outlook.com>

15/07/2019 17:35, Jerin Jacob Kollanukkaran:
> From: Thomas Monjalon <thomas@monjalon.net>
> > 15/07/2019 16:26, Jerin Jacob Kollanukkaran:
> > > > > Is there any specific reason why we always prefer PA if physical
> > > > > addresses are available? Since we're already assuming that all
> > > > > devices support PA and VA anyway, what's the harm in enabling VA by
> > default?
> > > >
> > > > If PA is available, it means we are running as root.
> > > > We can assume that using root is a choice, probably related to a
> > > > preference for PA.
> > >
> > > # Even if we are running as root, Why to choose PA in case of DC?
> > > ie. Following logic is not need
> > >                 if (iova_mode == RTE_IOVA_DC) {
> > >                         iova_mode = phys_addrs ? RTE_IOVA_PA : RTE_IOVA_VA;
> > >                         RTE_LOG(DEBUG, EAL,
> > >                                 "Buses did not request a specific IOVA mode, using '%s'
> > based on physical addresses availability.\n",
> > >                                 phys_addrs ? "PA" : "VA");
> > >                 }
> > 
> > Why running as root if using VA anyway?
> > We can assume the user knows what he is doing, so it is a user choice.
> > We want to allow the user choosing, right?
> 
> The user can override iova=pa/va as eal argument if user needs to run a specific mode.
> Running as root for various other reason(just be lazy) etc. it is not or it should not
> be connected to set the mode as PA.

Good point.
I tend to prefer avoiding the use of EAL arguments because they may
be unavailable, depending on the application.

> > > # When DPDK running on guest, Anyway it can not access the real PA, It will
> > be IPA.
> > 
> > What is IPA? Isn't it a beer?
> 
> There may a beer with that name. In this context, it is "Intermediate physical address"
> 
> > > So I don't understand logic behind choose PA when DC.
> > > To me, it make sense to choose PA when DC.
> > 
> > You probably mean "choose VA".
> 
> Yup.
> 
> > > # To align with RTE_PCI_DRV_NEED_MAPPING flag and reflect it "need"
> > > rather than support, I think, flag can be changed to
> > > RTE_PCI_DRV_NEED_IOVA_AS_VA
> > 
> > I think the most important is to have a good documentation of this flag (it
> > was not done properly when Cavium introduced it initially).
> > If you want to rename the flag, you can do it in a separate patch.
> > If renaming, I really would like to get an answer to an old question:
> > Why IO adress is called IOVA? The name "IOVA_AS_VA" looks strange.
> 
> IOVA = IO virtual address
> Since IOVA can be PA or VA, the name IOVA_AS_VA as chosen 

We could also call it "bus address" or "device address".
I think the word "IOVA" was enforced by Linux.
Anyway, my real issue when using "virtual" is that we don't really
know what we are talking about: is it an IOMMU translated address
on the device side or an MMU translated address on the application side?

I think we should better explain things.
One diagram which can help:
https://en.wikipedia.org/wiki/Input%E2%80%93output_memory_management_unit#/media/File:MMU_and_IOMMU.svg

> > For reference, one description of addressing:
> > https://lists.linuxfoundation.org/pipermail/iommu/2018-May/027686.html
> > 
> > About the naming, do you remember how I insisted to have a correct naming
> > of all related stuff in DPDK? It was hard to get it accepted, the discussion was
> > not nice and I stopped insisting to get all details fine because I just got bored.
> > It was a really bad experience.
> 
> I agree.
> To me that bad experience was due to mostly not having enough technical comments
> On the proposal. Though I am not the author/owner of it.
> 
> > You can ask why I remind this now? Because we must take care of all details,
> > make sure our messages are well understood, and be cooperative.
> 
> No disagreement.
> If we see the history the meaning got changed/updated in this commit
> By adding intel drivers to it. I would nt say  it is big ideal, It just C code,
> It can be changed based on the need. I think, what really import is,
> maintain the the feature and commitment towards fixing any issue.
> 
> commit f37dfab21c988d2d0ecb3c82be4ba9738c7e51c7
> Author: Jianfeng Tan <jianfeng.tan@intel.com>
> Date:   Wed Oct 11 10:33:48 2017 +0000
> 
>     drivers/net: enable IOVA mode for Intel PMDs
> 
>     If we want to enable IOVA mode, introduced by
>     commit 93878cf0255e ("eal: introduce helper API for IOVA mode"),
>     we need PMDs (for PCI devices) to expose this flag.
> 
>     Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
>     Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
>     Reviewed-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>

The doxygen meaning did not change from day one:
	/** Device driver supports IOVA as VA */
But the commit log meaning was:
	"Flag used when driver needs to operate in iova=va mode."
And the Intel commit log had a different understanding:
	"If we want to enable IOVA mode, [..] we need PMDs [..] to expose this flag."

Anyway we agree on the new meaning to be the original one the author
had in mind (i.e. "driver needs").

> > > Other than above points,
> > > Reviewed this patch and tested on octeontx2, It looks good to me.




  reply index

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-10 21:48 [dpdk-dev] [PATCH 0/2] Fixes on IOVA mode selection David Marchand
2019-07-10 21:48 ` [dpdk-dev] [PATCH 1/2] Revert "bus/pci: add Mellanox kernel driver type" David Marchand
2019-07-16 10:37   ` [dpdk-dev] [EXT] " Jerin Jacob Kollanukkaran
2019-07-10 21:48 ` [dpdk-dev] [PATCH 2/2] eal: fix IOVA mode selection as VA for pci drivers David Marchand
2019-07-11 14:40   ` Thomas Monjalon
2019-07-12  8:05     ` Jerin Jacob Kollanukkaran
2019-07-12 11:03   ` Burakov, Anatoly
2019-07-12 12:43     ` Thomas Monjalon
2019-07-12 12:58       ` Burakov, Anatoly
2019-07-12 13:19         ` Bruce Richardson
2019-07-15 14:26       ` Jerin Jacob Kollanukkaran
2019-07-15 15:03         ` Thomas Monjalon
2019-07-15 15:35           ` Jerin Jacob Kollanukkaran
2019-07-15 16:06             ` Thomas Monjalon [this message]
2019-07-15 16:27               ` Jerin Jacob Kollanukkaran
2019-07-16 13:46 ` [dpdk-dev] [PATCH v2 0/4] Fixes on IOVA mode selection jerinj
2019-07-16 13:46   ` [dpdk-dev] [PATCH v2 1/4] Revert "bus/pci: add Mellanox kernel driver type" jerinj
2019-07-16 13:46   ` [dpdk-dev] [PATCH v2 2/4] eal: fix IOVA mode selection as VA for pci drivers jerinj
2019-07-16 14:26     ` Burakov, Anatoly
2019-07-16 15:07       ` Jerin Jacob Kollanukkaran
2019-07-16 13:46   ` [dpdk-dev] [PATCH v2 3/4] eal: change RTE_PCI_DRV_IOVA_AS_VA flag name jerinj
2019-07-16 13:46   ` [dpdk-dev] [PATCH v2 4/4] eal: select IOVA mode as VA for default case jerinj
2019-07-16 14:33     ` Burakov, Anatoly
2019-07-17  8:33       ` [dpdk-dev] [EXT] " Jerin Jacob Kollanukkaran
2019-07-17 12:38         ` Burakov, Anatoly
2019-07-17 14:04           ` Jerin Jacob Kollanukkaran
2019-07-18  6:45   ` [dpdk-dev] [PATCH v3 0/4] Fixes on IOVA mode selection jerinj
2019-07-18  6:45     ` [dpdk-dev] [PATCH v3 1/4] Revert "bus/pci: add Mellanox kernel driver type" jerinj
2019-07-18  6:45     ` [dpdk-dev] [PATCH v3 2/4] eal: fix IOVA mode selection as VA for pci drivers jerinj
2019-07-18  6:45     ` [dpdk-dev] [PATCH v3 3/4] eal: change RTE_PCI_DRV_IOVA_AS_VA flag name jerinj
2019-07-18  6:45     ` [dpdk-dev] [PATCH v3 4/4] eal: select IOVA mode as VA for default case jerinj
2019-07-22 11:28     ` [dpdk-dev] [PATCH v3 0/4] Fixes on IOVA mode selection David Marchand
2019-07-22 12:56 ` [dpdk-dev] [PATCH v4 " David Marchand
2019-07-22 12:56   ` [dpdk-dev] [PATCH v4 1/4] Revert "bus/pci: add Mellanox kernel driver type" David Marchand
2019-07-22 12:56   ` [dpdk-dev] [PATCH v4 2/4] eal: fix IOVA mode selection as VA for PCI drivers David Marchand
2019-11-25  9:33     ` Ferruh Yigit
2019-11-25 10:22       ` Thomas Monjalon
2019-11-25 12:03         ` Ferruh Yigit
2019-11-25 12:36           ` David Marchand
2019-11-25 12:58             ` Burakov, Anatoly
2019-11-25 14:29               ` Thomas Monjalon
2019-11-25 11:07       ` Jerin Jacob
2019-07-22 12:56   ` [dpdk-dev] [PATCH v4 3/4] drivers: change IOVA as VA PCI flag name David Marchand
2019-07-22 12:56   ` [dpdk-dev] [PATCH v4 4/4] eal: select IOVA as VA mode for default case David Marchand
2019-07-22 15:53   ` [dpdk-dev] [PATCH v4 0/4] Fixes on IOVA mode selection Thomas Monjalon
2019-07-23  3:35     ` Stojaczyk, Dariusz
2019-07-23  4:18       ` Jerin Jacob Kollanukkaran
2019-07-23  4:54         ` Stojaczyk, Dariusz
2019-07-23  5:27           ` Jerin Jacob Kollanukkaran
2019-07-23  7:21             ` Thomas Monjalon
2019-07-23  9:57             ` Burakov, Anatoly
2019-07-23 10:25               ` Thomas Monjalon
2019-07-23 13:56                 ` Burakov, Anatoly
2019-07-23 14:24                   ` [dpdk-dev] [EXT] " Jerin Jacob Kollanukkaran
2019-07-23 14:29                   ` [dpdk-dev] " Burakov, Anatoly
2019-07-23 14:36                     ` [dpdk-dev] [EXT] " Jerin Jacob Kollanukkaran
2019-07-23 15:47                       ` Burakov, Anatoly

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