From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Tom Herbert <tom@herbertland.com>,
Brenden Blanco <bblanco@plumgrid.com>,
"David S. Miller" <davem@davemloft.net>,
Linux Kernel Network Developers <netdev@vger.kernel.org>,
Jamal Hadi Salim <jhs@mojatatu.com>,
Saeed Mahameed <saeedm@dev.mellanox.co.il>,
Martin KaFai Lau <kafai@fb.com>, Ari Saha <as754m@att.com>,
Or Gerlitz <gerlitz.or@gmail.com>,
john fastabend <john.fastabend@gmail.com>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
Thomas Graf <tgraf@suug.ch>,
Daniel Borkmann <daniel@iogearbox.net>,
brouer@redhat.com
Subject: Re: [PATCH v8 04/11] net/mlx4_en: add support for fast rx drop bpf program
Date: Fri, 15 Jul 2016 21:09:52 +0200 [thread overview]
Message-ID: <20160715210952.089a793e@redhat.com> (raw)
In-Reply-To: <20160715164744.GA3693@ast-mbp.thefacebook.com>
On Fri, 15 Jul 2016 09:47:46 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> On Fri, Jul 15, 2016 at 09:18:13AM -0700, Tom Herbert wrote:
[..]
> > > We don't need extra comlexity of figuring out number of rings and
> > > struggling with lack of atomicity.
> >
> > We already have this problem with other per ring configuration.
>
> not really. without atomicity of the program change, the user space
> daemon that controls it will struggle to adjust. Consider the case
> where we're pushing new update for loadbalancer. In such case we
> want to reuse the established bpf map, since we cannot atomically
> move it from old to new, but we want to swap the program that uses
> in one go, otherwise two different programs will be accessing
> the same map. Technically it's valid, but difference in the programs
> may cause issues. Lack of atomicity is not intractable problem,
> it just makes user space quite a bit more complex for no reason.
I don't think you have a problem with updating the program per queue
basis, as they will be updated atomically per RX queue (thus a CPU can
only see one program).
Today, you already have to handle that multiple CPUs running the same
program, need to access the same map.
You mention that, there might be a problem, if the program differs too
much to share the map. But that is the same problem as today. If you
need to load a program that e.g. change the map layout, then you
obviously cannot allow it inherit the old map, but must feed the new
program a new map (with the new layout).
There is actually a performance advantage of knowing that a program is
only attached to a single RX queue. As only a single CPU can process a
RX ring. Thus, when e.g. accessing a map (or other lookup table) you can
avoid any locking.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2016-07-15 19:10 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-12 7:51 [PATCH v8 00/11] Add driver bpf hook for early packet drop and forwarding Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 01/11] bpf: add XDP prog type for early driver filter Brenden Blanco
2016-07-12 13:14 ` Jesper Dangaard Brouer
2016-07-12 14:52 ` Tom Herbert
2016-07-12 16:08 ` Jakub Kicinski
2016-07-13 4:14 ` Alexei Starovoitov
2016-07-12 7:51 ` [PATCH v8 02/11] net: add ndo to setup/query xdp prog in adapter rx Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 03/11] rtnl: add option for setting link xdp prog Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 04/11] net/mlx4_en: add support for fast rx drop bpf program Brenden Blanco
2016-07-12 12:02 ` Tariq Toukan
2016-07-13 11:27 ` David Laight
2016-07-13 14:08 ` Brenden Blanco
2016-07-14 7:25 ` Jesper Dangaard Brouer
2016-07-15 3:30 ` Alexei Starovoitov
2016-07-15 8:21 ` Jesper Dangaard Brouer
2016-07-15 16:56 ` Alexei Starovoitov
2016-07-15 16:18 ` Tom Herbert
2016-07-15 16:47 ` Alexei Starovoitov
2016-07-15 17:49 ` Tom Herbert
2016-07-18 9:10 ` Thomas Graf
2016-07-18 11:39 ` Tom Herbert
2016-07-18 12:48 ` Thomas Graf
2016-07-18 13:07 ` Tom Herbert
2016-07-19 2:45 ` Alexei Starovoitov
2016-07-18 19:03 ` Brenden Blanco
2016-07-15 19:09 ` Jesper Dangaard Brouer [this message]
2016-07-18 4:01 ` Alexei Starovoitov
2016-07-18 8:35 ` Daniel Borkmann
2016-07-15 18:08 ` Tom Herbert
2016-07-15 18:45 ` Jesper Dangaard Brouer
2016-07-12 7:51 ` [PATCH v8 05/11] Add sample for adding simple drop program to link Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 06/11] net/mlx4_en: add page recycle to prepare rx ring for tx support Brenden Blanco
2016-07-12 12:09 ` Tariq Toukan
2016-07-12 21:18 ` David Miller
2016-07-13 0:54 ` Brenden Blanco
2016-07-13 7:17 ` Tariq Toukan
2016-07-13 15:40 ` Brenden Blanco
2016-07-15 21:52 ` Brenden Blanco
[not found] ` <6d638467-eea6-d3e1-6984-88a1198ef303@gmail.com>
2016-07-19 17:41 ` Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 07/11] bpf: add XDP_TX xdp_action for direct forwarding Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 08/11] net/mlx4_en: break out tx_desc write into separate function Brenden Blanco
2016-07-12 12:16 ` Tariq Toukan
2016-07-12 7:51 ` [PATCH v8 09/11] net/mlx4_en: add xdp forwarding and data write support Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 10/11] bpf: enable direct packet data write for xdp progs Brenden Blanco
2016-07-12 7:51 ` [PATCH v8 11/11] bpf: add sample for xdp forwarding and rewrite Brenden Blanco
2016-07-12 14:38 ` [PATCH v8 00/11] Add driver bpf hook for early packet drop and forwarding Tariq Toukan
2016-07-13 15:00 ` Tariq Toukan
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