From: Jesper Dangaard Brouer <brouer@redhat•com>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: Rick Jones <rick.jones2@hpe•com>,
netdev@vger•kernel.org, brouer@redhat•com
Subject: Re: Netperf UDP issue with connected sockets
Date: Thu, 17 Nov 2016 15:57:53 +0100 [thread overview]
Message-ID: <20161117155753.17b76f5a@redhat.com> (raw)
In-Reply-To: <1479392258.8455.249.camel@edumazet-glaptop3.roam.corp.google.com>
On Thu, 17 Nov 2016 06:17:38 -0800
Eric Dumazet <eric.dumazet@gmail•com> wrote:
> On Thu, 2016-11-17 at 14:42 +0100, Jesper Dangaard Brouer wrote:
>
> > I can see that qdisc layer does not activate xmit_more in this case.
> >
>
> Sure. Not enough pressure from the sender(s).
>
> The bottleneck is not the NIC or qdisc in your case, meaning that BQL
> limit is kept at a small value.
>
> (BTW not all NIC have expensive doorbells)
I believe this NIC mlx5 (50G edition) does.
I'm seeing UDP TX of 1656017.55 pps, which is per packet:
2414 cycles(tsc) 603.86 ns
Perf top shows (with my own udp_flood, that avoids __ip_select_ident):
Samples: 56K of event 'cycles', Event count (approx.): 51613832267
Overhead Command Shared Object Symbol
+ 8.92% udp_flood [kernel.vmlinux] [k] _raw_spin_lock
- _raw_spin_lock
+ 90.78% __dev_queue_xmit
+ 7.83% dev_queue_xmit
+ 1.30% ___slab_alloc
+ 5.59% udp_flood [kernel.vmlinux] [k] skb_set_owner_w
+ 4.77% udp_flood [mlx5_core] [k] mlx5e_sq_xmit
+ 4.09% udp_flood [kernel.vmlinux] [k] fib_table_lookup
+ 4.00% swapper [mlx5_core] [k] mlx5e_poll_tx_cq
+ 3.11% udp_flood [kernel.vmlinux] [k] __ip_route_output_key_hash
+ 2.49% swapper [kernel.vmlinux] [k] __slab_free
In this setup the spinlock in __dev_queue_xmit should be uncongested.
An uncongested spin_lock+unlock cost 32 cycles(tsc) 8.198 ns on this system.
But 8.92% of the time is spend on it, which corresponds to a cost of 215
cycles (2414*0.0892). This cost is too high, thus something else is
going on... I claim this mysterious extra cost is the tailptr/doorbell.
--
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:[~2016-11-17 17:26 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-03 14:59 High perf top ip_idents_reserve doing netperf UDP_STREAM Jesper Dangaard Brouer
2014-09-03 15:17 ` Eric Dumazet
2016-11-16 12:16 ` Netperf UDP issue with connected sockets Jesper Dangaard Brouer
2016-11-16 17:46 ` Rick Jones
2016-11-16 22:40 ` Jesper Dangaard Brouer
2016-11-16 22:50 ` Rick Jones
2016-11-17 0:34 ` Eric Dumazet
2016-11-17 8:16 ` Jesper Dangaard Brouer
2016-11-17 13:20 ` Eric Dumazet
2016-11-17 13:42 ` Jesper Dangaard Brouer
2016-11-17 14:17 ` Eric Dumazet
2016-11-17 14:57 ` Jesper Dangaard Brouer [this message]
2016-11-17 16:21 ` Eric Dumazet
2016-11-17 18:30 ` Jesper Dangaard Brouer
2016-11-17 18:51 ` Eric Dumazet
2016-11-17 21:19 ` Jesper Dangaard Brouer
2016-11-17 21:44 ` Eric Dumazet
2016-11-17 23:08 ` Rick Jones
2016-11-18 0:37 ` Julian Anastasov
2016-11-18 0:42 ` Rick Jones
2016-11-18 17:12 ` Jesper Dangaard Brouer
2016-11-21 16:03 ` Jesper Dangaard Brouer
2016-11-21 18:10 ` Eric Dumazet
2016-11-29 6:58 ` [WIP] net+mlx4: auto doorbell Eric Dumazet
2016-11-30 11:38 ` Jesper Dangaard Brouer
2016-11-30 15:56 ` Eric Dumazet
2016-11-30 19:17 ` Jesper Dangaard Brouer
2016-11-30 19:30 ` Eric Dumazet
2016-11-30 22:30 ` Jesper Dangaard Brouer
2016-11-30 22:40 ` Eric Dumazet
2016-12-01 0:27 ` Eric Dumazet
2016-12-01 1:16 ` Tom Herbert
2016-12-01 2:32 ` Eric Dumazet
2016-12-01 2:50 ` Eric Dumazet
2016-12-02 18:16 ` Eric Dumazet
2016-12-01 5:03 ` Tom Herbert
2016-12-01 19:24 ` Willem de Bruijn
2016-11-30 13:50 ` Saeed Mahameed
2016-11-30 15:44 ` Eric Dumazet
2016-11-30 16:27 ` Saeed Mahameed
2016-11-30 17:28 ` Eric Dumazet
2016-12-01 12:05 ` Jesper Dangaard Brouer
2016-12-01 14:24 ` Eric Dumazet
2016-12-01 16:04 ` Jesper Dangaard Brouer
2016-12-01 17:04 ` Eric Dumazet
2016-12-01 19:17 ` Jesper Dangaard Brouer
2016-12-01 20:11 ` Eric Dumazet
2016-12-01 20:20 ` David Miller
2016-12-01 22:10 ` Eric Dumazet
2016-12-02 14:23 ` Eric Dumazet
2016-12-01 21:32 ` Alexander Duyck
2016-12-01 22:04 ` Eric Dumazet
2016-11-17 17:34 ` Netperf UDP issue with connected sockets David Laight
2016-11-17 22:39 ` Alexander Duyck
2016-11-17 17:42 ` Rick Jones
2016-11-28 18:33 ` Rick Jones
2016-11-28 18:40 ` Rick Jones
2016-11-30 10:43 ` Jesper Dangaard Brouer
2016-11-30 17:42 ` Rick Jones
2016-11-30 18:11 ` David Miller
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