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Date: Tue, 27 Mar 2018 08:09:53 +0200
From: Björn Töpel <bjorn.topel@...il.com>
To: William Tu <u9012063@...il.com>
Cc: Jesper Dangaard Brouer <brouer@...hat.com>,
"Karlsson, Magnus" <magnus.karlsson@...el.com>,
Alexander Duyck <alexander.h.duyck@...el.com>,
Alexander Duyck <alexander.duyck@...il.com>,
John Fastabend <john.fastabend@...il.com>,
Alexei Starovoitov <ast@...com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
Björn Töpel <bjorn.topel@...el.com>,
michael.lundkvist@...csson.com,
"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
"Singhai, Anjali" <anjali.singhai@...el.com>,
"Shaw, Jeffrey B" <jeffrey.b.shaw@...el.com>,
"Yigit, Ferruh" <ferruh.yigit@...el.com>,
"Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [RFC PATCH 00/24] Introducing AF_XDP support
2018-03-26 23:58 GMT+02:00 William Tu <u9012063@...il.com>:
> Hi Jesper,
>
> Thanks a lot for your prompt reply.
>
>>> Hi,
>>> I also did an evaluation of AF_XDP, however the performance isn't as
>>> good as above.
>>> I'd like to share the result and see if there are some tuning suggestions.
>>>
>>> System:
>>> 16 core, Intel(R) Xeon(R) CPU E5-2440 v2 @ 1.90GHz
>>> Intel 10G X540-AT2 ---> so I can only run XDP_SKB mode
>>
>> Hmmm, why is X540-AT2 not able to use XDP natively?
>
> Because I'm only able to use ixgbe driver for this NIC,
> and AF_XDP patch only has i40e support?
>
It's only i40e that support zero copy. As for native XDP support, only
XDP_REDIRECT support is required and ixgbe does support XDP_REDIRECT
-- unfortunately, ixgbe still needs a needs a patch to work properly,
which is in net-next: ed93a3987128 ("ixgbe: tweak page counting for
XDP_REDIRECT").
>>
>>> AF_XDP performance:
>>> Benchmark XDP_SKB
>>> rxdrop 1.27 Mpps
>>> txpush 0.99 Mpps
>>> l2fwd 0.85 Mpps
>>
>> Definitely too low...
>>
> I did another run, the rxdrop seems better.
> Benchmark XDP_SKB
> rxdrop 2.3 Mpps
> txpush 1.05 Mpps
> l2fwd 0.90 Mpps
>
>> What is the performance if you drop packets via iptables?
>>
>> Command:
>> $ iptables -t raw -I PREROUTING -p udp --dport 9 --j DROP
>>
> I did
> # iptables -t raw -I PREROUTING -p udp -i enp10s0f0 -j DROP
> # iptables -nvL -t raw; sleep 10; iptables -nvL -t raw
>
> and I got 2.9Mpps.
>
>>> NIC configuration:
>>> the command
>>> "ethtool -N p3p2 flow-type udp4 src-port 4242 dst-port 4242 action 16"
>>> doesn't work on my ixgbe driver, so I use ntuple:
>>>
>>> ethtool -K enp10s0f0 ntuple on
>>> ethtool -U enp10s0f0 flow-type udp4 src-ip 10.1.1.100 action 1
>>> then
>>> echo 1 > /proc/sys/net/core/bpf_jit_enable
>>> ./xdpsock -i enp10s0f0 -r -S --queue=1
>>>
>>> I also take a look at perf result:
>>> For rxdrop:
>>> 86.56% xdpsock xdpsock [.] main
>>> 9.22% xdpsock [kernel.vmlinux] [k] nmi
>>> 4.23% xdpsock xdpsock [.] xq_enq
>>
>> It looks very strange that you see non-maskable interrupt's (NMI) being
>> this high...
>>
> yes, that's weird. Looking at the perf annotate of nmi,
> it shows 100% spent on nop instruction.
>
>>
>>> For l2fwd:
>>> 20.81% xdpsock xdpsock [.] main
>>> 10.64% xdpsock [kernel.vmlinux] [k] clflush_cache_range
>>
>> Oh, clflush_cache_range is being called!
>
> I though clflush_cache_range is high because we have many smp_rmb, smp_wmb
> in the xdpsock queue/ring management userspace code.
> (perf shows that 75% of this 10.64% spent on mfence instruction.)
>
>> Do your system use an IOMMU ?
>>
> Yes.
> With CONFIG_INTEL_IOMMU=y
> and I saw some related functions called (ex: intel_alloc_iova).
>
>>> 8.46% xdpsock [kernel.vmlinux] [k] xsk_sendmsg
>>> 6.72% xdpsock [kernel.vmlinux] [k] skb_set_owner_w
>>> 5.89% xdpsock [kernel.vmlinux] [k] __domain_mapping
>>> 5.74% xdpsock [kernel.vmlinux] [k] alloc_skb_with_frags
>>> 4.62% xdpsock [kernel.vmlinux] [k] netif_skb_features
>>> 3.96% xdpsock [kernel.vmlinux] [k] ___slab_alloc
>>> 3.18% xdpsock [kernel.vmlinux] [k] nmi
>>
>> Again high count for NMI ?!?
>>
>> Maybe you just forgot to tell perf that you want it to decode the
>> bpf_prog correctly?
>>
>> https://prototype-kernel.readthedocs.io/en/latest/bpf/troubleshooting.html#perf-tool-symbols
>>
>> Enable via:
>> $ sysctl net/core/bpf_jit_kallsyms=1
>>
>> And use perf report (while BPF is STILL LOADED):
>>
>> $ perf report --kallsyms=/proc/kallsyms
>>
>> E.g. for emailing this you can use this command:
>>
>> $ perf report --sort cpu,comm,dso,symbol --kallsyms=/proc/kallsyms --no-children --stdio -g none | head -n 40
>>
>
> Thanks, I followed the steps, the result of l2fwd
> # Total Lost Samples: 119
> #
> # Samples: 2K of event 'cycles:ppp'
> # Event count (approx.): 25675705627
> #
> # Overhead CPU Command Shared Object Symbol
> # ........ ... ....... .................. ..................................
> #
> 10.48% 013 xdpsock xdpsock [.] main
> 9.77% 013 xdpsock [kernel.vmlinux] [k] clflush_cache_range
> 8.45% 013 xdpsock [kernel.vmlinux] [k] nmi
> 8.07% 013 xdpsock [kernel.vmlinux] [k] xsk_sendmsg
> 7.81% 013 xdpsock [kernel.vmlinux] [k] __domain_mapping
> 4.95% 013 xdpsock [kernel.vmlinux] [k] ixgbe_xmit_frame_ring
> 4.66% 013 xdpsock [kernel.vmlinux] [k] skb_store_bits
> 4.39% 013 xdpsock [kernel.vmlinux] [k] syscall_return_via_sysret
> 3.93% 013 xdpsock [kernel.vmlinux] [k] pfn_to_dma_pte
> 2.62% 013 xdpsock [kernel.vmlinux] [k] __intel_map_single
> 2.53% 013 xdpsock [kernel.vmlinux] [k] __alloc_skb
> 2.36% 013 xdpsock [kernel.vmlinux] [k] iommu_no_mapping
> 2.21% 013 xdpsock [kernel.vmlinux] [k] alloc_skb_with_frags
> 2.07% 013 xdpsock [kernel.vmlinux] [k] skb_set_owner_w
> 1.98% 013 xdpsock [kernel.vmlinux] [k] __kmalloc_node_track_caller
> 1.94% 013 xdpsock [kernel.vmlinux] [k] ksize
> 1.84% 013 xdpsock [kernel.vmlinux] [k] validate_xmit_skb_list
> 1.62% 013 xdpsock [kernel.vmlinux] [k] kmem_cache_alloc_node
> 1.48% 013 xdpsock [kernel.vmlinux] [k] __kmalloc_reserve.isra.37
> 1.21% 013 xdpsock xdpsock [.] xq_enq
> 1.08% 013 xdpsock [kernel.vmlinux] [k] intel_alloc_iova
>
> And l2fwd under "perf stat" looks OK to me. There is little context
> switches, cpu
> is fully utilized, 1.17 insn per cycle seems ok.
>
> Performance counter stats for 'CPU(s) 6':
> 10000.787420 cpu-clock (msec) # 1.000 CPUs
> utilized
> 24 context-switches # 0.002 K/sec
> 0 cpu-migrations # 0.000 K/sec
> 0 page-faults # 0.000 K/sec
> 22,361,333,647 cycles # 2.236 GHz
> 13,458,442,838 stalled-cycles-frontend # 60.19% frontend
> cycles idle
> 26,251,003,067 instructions # 1.17 insn per
> cycle
> # 0.51 stalled
> cycles per insn
> 4,938,921,868 branches # 493.853 M/sec
> 7,591,739 branch-misses # 0.15% of all
> branches
> 10.000835769 seconds time elapsed
>
> Will continue investigate...
> Thanks
> William
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