Hi,
I've checked it further, based on Stephen's suggestion I've tried perf
top as well. The results were the same, it spends a lot of time in that
part of the code, and there are high number of branch load misses
(BR_MISS_PRED_RETIRED) around there too.
I've also started to strip down miniflow_extract() to remove parts which
are not relevant to this very simple testcase. I've removed the metadata
checking branches and the "size < sizeof(struct eth_header)". I've
removed the size check from emc_processing, and placed log messages in
flow_extract and netdev_flow_key_from_flow, to make sure the excessive
time spent in miniflow_extract is not because these two are somehow
calling it.
That way I've closed out all of the branches preceding this instruction.
Oddly the high sample number now moved down a few instructions:
...
dp_packet_reset_offsets
5113eb: b8 ff ff ff ff mov $0xffffffff,%eax
5113f0: 66 89 8f 86 00 00 00 mov %cx,0x86(%rdi)
5113f7: c6 87 81 00 00 00 00 movb $0x0,0x81(%rdi)
5113fe: 66 89 87 82 00 00 00 mov %ax,0x82(%rdi)
data_pull
511405: 48 8d 4d 0c lea 0xc(%rbp),%rcx
dp_packet_reset_offsets
511409: 66 89 97 84 00 00 00 mov %dx,0x84(%rdi)
memcpy
511410: 48 8b 45 00 mov 0x0(%rbp),%rax
511414: 48 89 46 18 mov %rax,0x18(%rsi)
This last instruction moves the first 8 bytes of the MAC address (coming
from 0x0(%rbp)) to 0x18(%rsi), which is basically memory pointed by
parameter "struct miniflow *dst". It is allocated on the stack by
emc_processing.
I couldn't find any branch which can cause this miss, but then I've
checked the PMD stats:
pmd thread numa_id 0 core_id 1:
emc hits:4395834176
megaflow hits:1
miss:1
lost:0
polling cycles:166083129380 (16.65%)
processing cycles:831536059972 (83.35%)
avg cycles per packet: 226.95 (997619189352/4395834178)
avg processing cycles per packet: 189.16 (831536059972/4395834178)
So everything hits EMC, when I measured the change of that counter for
10 seconds, the result was around ~13.3 Mpps too. The cycle statistics
shows that it should be able to handle more than 15M packets per second,
yet it doesn't receive that much, while with the non-vector PMD it can
max out the link.
Any more suggestions?
Regards,
Zoltan
On 21/08/15 19:05, Zoltan Kiss 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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