[dpdk-dev] OVS-DPDK performance problem on ixgbe vector PMD

Stephen Hemminger stephen at networkplumber.org
Fri Aug 21 22:25:36 CEST 2015


Use perf top it gives much better data than oprofile

On Fri, Aug 21, 2015 at 11:05 AM, Zoltan Kiss <zoltan.kiss at linaro.org>
wrote:

> Hi,
>
> I've set up a simple packet forwarding perf test on a dual-port 10G
> 82599ES: one port receives 64 byte UDP packets, the other sends it out, one
> core used. I've used latest OVS with DPDK 2.1, and the first result was
> only 13.2 Mpps, which was a bit far from the 13.9 I've seen last year with
> the same test. The first thing I've changed was to revert back to the old
> behaviour about this issue:
>
> http://permalink.gmane.org/gmane.comp.networking.dpdk.devel/22731
>
> So instead of the new default I've passed 2048 + RTE_PKTMBUF_HEADROOM.
> That increased the performance to 13.5, but to figure out what's wrong
> started to play with the receive functions. First I've disabled vector PMD,
> but ixgbe_recv_pkts_bulk_alloc() was even worse, only 12.5 Mpps. So then
> I've enabled scattered RX, and with ixgbe_recv_pkts_lro_bulk_alloc() I
> could manage to get 13.98 Mpps, which is I guess as close as possible to
> the 14.2 line rate (on my HW at least, with one core)
> Does anyone has a good explanation about why the vector PMD performs so
> significantly worse? I would expect that on a 3.2 GHz i5-4570 one core
> should be able to reach ~14 Mpps, SG and vector PMD shouldn't make a
> difference.
> I've tried to look into it with oprofile, but the results were quite
> strange: 35% of the samples were from miniflow_extract, the part where
> parse_vlan calls data_pull to jump after the MAC addresses. The oprofile
> snippet (1M samples):
>
>   511454 19        0.0037  flow.c:511
>   511458 149       0.0292  dp-packet.h:266
>   51145f 4264      0.8357  dp-packet.h:267
>   511466 18        0.0035  dp-packet.h:268
>   51146d 43        0.0084  dp-packet.h:269
>   511474 172       0.0337  flow.c:511
>   51147a 4320      0.8467  string3.h:51
>   51147e 358763   70.3176  flow.c:99
>   511482 2        3.9e-04  string3.h:51
>   511485 3060      0.5998  string3.h:51
>   511488 1693      0.3318  string3.h:51
>   51148c 2933      0.5749  flow.c:326
>   511491 47        0.0092  flow.c:326
>
> And the corresponding disassembled code:
>
>   511454:       49 83 f9 0d             cmp    r9,0xd
>   511458:       c6 83 81 00 00 00 00    mov    BYTE PTR [rbx+0x81],0x0
>   51145f:       66 89 83 82 00 00 00    mov    WORD PTR [rbx+0x82],ax
>   511466:       66 89 93 84 00 00 00    mov    WORD PTR [rbx+0x84],dx
>   51146d:       66 89 8b 86 00 00 00    mov    WORD PTR [rbx+0x86],cx
>   511474:       0f 86 af 01 00 00       jbe    511629
> <miniflow_extract+0x279>
>   51147a:       48 8b 45 00             mov    rax,QWORD PTR [rbp+0x0]
>   51147e:       4c 8d 5d 0c             lea    r11,[rbp+0xc]
>   511482:       49 89 00                mov    QWORD PTR [r8],rax
>   511485:       8b 45 08                mov    eax,DWORD PTR [rbp+0x8]
>   511488:       41 89 40 08             mov    DWORD PTR [r8+0x8],eax
>   51148c:       44 0f b7 55 0c          movzx  r10d,WORD PTR [rbp+0xc]
>   511491:       66 41 81 fa 81 00       cmp    r10w,0x81
>
> My only explanation to this so far is that I misunderstand something about
> the oprofile results.
>
> Regards,
>
> Zoltan
>


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