From: Jesper Dangaard Brouer <brouer@redhat.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
Netdev <netdev@vger.kernel.org>,
Tom Herbert <tom@herbertland.com>,
Alexei Starovoitov <ast@kernel.org>,
John Fastabend <john.r.fastabend@intel.com>,
Daniel Borkmann <daniel@iogearbox.net>,
brouer@redhat.com, David Miller <davem@davemloft.net>
Subject: Re: Questions on XDP
Date: Sat, 18 Feb 2017 17:34:02 +0100 [thread overview]
Message-ID: <20170218173402.1af86005@redhat.com> (raw)
In-Reply-To: <58A62979.1050600@gmail.com>
On Thu, 16 Feb 2017 14:36:41 -0800
John Fastabend <john.fastabend@gmail.com> wrote:
> On 17-02-16 12:41 PM, Alexander Duyck wrote:
> > So I'm in the process of working on enabling XDP for the Intel NICs
> > and I had a few questions so I just thought I would put them out here
> > to try and get everything sorted before I paint myself into a corner.
> >
> > So my first question is why does the documentation mention 1 frame per
> > page for XDP?
Yes, XDP defines upfront a memory model where there is only one packet
per page[1], please respect that!
This is currently used/needed for fast-direct recycling of pages inside
the driver for XDP_DROP and XDP_TX, _without_ performing any atomic
refcnt operations on the page. E.g. see mlx4_en_rx_recycle().
This is also about controlling the cache-coherency state of the
struct-page cache-line. (With two (or-more) packets per page,
the struct-page cache-line will be jumping around.) Controlling this is
essential when packets are transferred between CPUs. We need an
architecture were we can control this, please.
[1] https://prototype-kernel.readthedocs.io/en/latest/networking/XDP/design/requirements.html#page-per-packet
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2017-02-18 16:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-16 20:41 Questions on XDP Alexander Duyck
2017-02-16 22:36 ` John Fastabend
2017-02-18 16:34 ` Jesper Dangaard Brouer [this message]
2017-02-18 17:41 ` Eric Dumazet
2017-02-18 18:18 ` Alexander Duyck
2017-02-18 23:28 ` John Fastabend
2017-02-18 23:31 Alexei Starovoitov
2017-02-18 23:48 ` John Fastabend
2017-02-18 23:59 ` Eric Dumazet
2017-02-19 2:16 ` Alexander Duyck
2017-02-19 3:48 ` John Fastabend
2017-02-20 20:06 ` Jakub Kicinski
2017-02-22 5:02 ` John Fastabend
2017-02-21 3:18 ` Alexei Starovoitov
2017-02-21 3:39 ` John Fastabend
2017-02-21 4:00 ` Alexander Duyck
2017-02-21 7:55 ` Alexei Starovoitov
2017-02-21 17:44 ` Alexander Duyck
2017-02-22 17:08 ` John Fastabend
2017-02-22 21:59 ` Jesper Dangaard Brouer
2017-02-18 23:59 Alexei Starovoitov
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