netdev - Re: [PATCH rdma-next 0/8] User space steering

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Message-ID: <20190402101000.5eeaef72@cakuba.hsd1.ca.comcast.net>
Date:   Tue, 2 Apr 2019 10:10:00 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Ariel Levkovich <lariel@...lanox.com>,
        Eli Cohen <eli@...lanox.com>, Mark Bloch <markb@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next 0/8] User space steering

On Tue, 2 Apr 2019 11:14:59 +0300, Leon Romanovsky wrote:
> On Mon, Apr 01, 2019 at 11:32:21AM -0700, Jakub Kicinski wrote:
> > On Mon, 1 Apr 2019 09:28:16 +0300, Leon Romanovsky wrote:  
> > > On Sun, Mar 31, 2019 at 02:06:33PM -0700, Jakub Kicinski wrote:  
> > > > On Sun, 31 Mar 2019 19:44:42 +0300, Leon Romanovsky wrote:  
> > > > > From: Leon Romanovsky <leonro@...lanox.com>
> > > > >
> > > > > From Ariel,
> > > > >
> > > > > This series of patches adds user space managed steering infrastructure
> > > > > to the mlx5_ib driver.
> > > > >
> > > > > User space managed steering requires the means to access a dedicated
> > > > > memory space that is used by the device to store the packet steering
> > > > > and header modification tables and rules in order to manage them directly
> > > > > without the device's firmware involvement. This dedicated memory is part
> > > > > of the ICM memory space.
> > > > >
> > > > > The changes are introducing the mlx5_ib API to allocate, deallocate and
> > > > > register this dedicated SW ICM memory via the existing device memory API
> > > > > using a private attribute which specifies the memory type.
> > > > >
> > > > > The allocated memory itself is not IO mapped and user can only access it
> > > > > using remote RDMA operations.
> > > > >
> > > > > In addition, the series exposed the ICM address of the receive transport
> > > > > interface (TIR) of Raw Packet and RSS QPs to user since they are required
> > > > > to properly create and insert steering rules that direct flows to these QPs.  
> > > >
> > > > Hi Leon!  Out of curiosity what protocols are you guys steering here?
> > > > Is this some form of RoCE or IB?  Is there a good resource to read up on
> > > > the DEVX stuff? (I presume this series is related?)  
> > >
> > > mlx5 devices steering operates on packets without relation to specific
> > > protocol. The decision to steer is based on HW capabilities and user
> > > configuration for matching specific fields. Such configuration is done
> > > through kernel and through DEVX.
> > >
> > > General description of DEVX can be found in manuals of libmlx5.
> > > https://github.com/linux-rdma/rdma-core/blob/master/providers/mlx5/man/mlx5dv_devx_obj_create.3.md
> > > https://github.com/linux-rdma/rdma-core/blob/master/providers/mlx5/man/  
> >
> > Thanks for those, looks quite powerful.  What's your primary use case
> > here?  Is there some flow steering and encapsulation going on in RDMA
> > world?  
> 
> Usual use case for that is in RoCE fabric, but as I said it is not
> limited to that. For example, flow steering is used in libpcap [1]
> and encapsulation is used for efficient VM to VM communication over
> different hosts (I assume exactly as in netdev world).
> 
> In regarding to this patch set, the combination of this steering
> functionality with DEVX allows us to speedup greatly buildup of rules
> by doing it in powerful host CPU instead of internal to NIC CPU.
> 
> [1]
> https://github.com/the-tcpdump-group/libpcap/commit/f5f1484a931851d2d3b67d6033aedea8da5acb42

Interesting, thanks for the info!