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PISCES: A Programmable,Protocol-Independent Software Switch
Muhammad Shahbaz, Sean Choi, Ben Pfaff, Changhoon Kim,Nick Feamster, Nick McKeown, and Jennifer Rexford
TCP
IPv4
Ethernet
UDP
IPv6 BGP
HTTP
TLS
Fixed-Function Switch ChipFixed Set of Protocols
• Ease of Adding new protocols
• Ease of Removing unused protocols
• Gain greater Visibility into the network
• Fold network functions into the switch
TCP
IPv4
Ethernet
CUSTOM_P
IPv6 BGP
HTTP
TLS
Programmable Switching ChipCustom Protocols
Hypervisor Switch
VM VM
3 Virtual Ports
1 Physical Port
0
20
40
60
2010 2011 2012 2013 2014 2015
Approx. Number of Physical Ports vs. Virtual Ports [1]
Phyical Ports Virtual Ports
[1] Martin Casado, VMWorld 2013
Not really…
It should be EASY to program software switches!
Fast Packet Forwarding
Software Switch
KernelDPDK
Packet Processing Logic
Software Switch
KernelDPDK
Parser Match-Action Pipeline
Requires domain expertise in:
- Network protocol design
- Kernel development
Slow to release changesSpecialized APIs
Software Switch
KernelDPDK
Parser Match-Action Pipeline
Adding TCP Flag in Open vSwitchrequired changes in…
20 Files and 370 Lines of Code![1]
Weeks of Development and Test
[1] https://github.com/openvswitch/ovs/commit/dc235f7fbcff
We can do this in 4 lines and within minutes with PISCES!
header_type tcpv2_t {
fields {
srcPort : 16;
dstPort : 16;
seqNo : 32;
ackNo : 32;
dataOffset : 4;
res : 4;
tcp_flags : 12;
window : 16;
checksum : 16;
urgentPtr : 16;
}
}
parser tcpv2 {
extract(tcpv2);
set_metadata(flow.tcp_flags,
tcpv2.tcp_flags);
return ingress;
}
header_type flow_t {
fields {
...
tcp_flags_pad : 4;
tcp_flags : 12;
...
}
}
KernelDPDK
Software Switch
Parser Match-Action Pipeline
KernelDPDK
Software Switch
Domain-Specific Language (DSL)
Parser Match-Action Pipeline
Compile
Parser Match-Action Pipeline
TCP Header
header_type tcp_t {
fields {
srcPort : 16;
dstPort : 16;
seqNo : 32;
ackNo : 32;
dataOffset : 4;
res : 4;
window : 16;
checksum : 16;
urgentPtr : 16;
}
}
parser tcp {
extract(tcp);
return ingress;
}
...
KernelDPDK
Software Switch
Domain-Specific Language
Parser Match-Action Pipeline
Compile
Parser Match-Action Pipeline
Domain-Specific Language 2
Parser Match-Action Pipeline
KernelDPDK
Switch 2
Parser Match-Action Pipeline
PISCES is an implementation with a
• Specific Domain-Specific Language
• Specific Software Switch Target
KernelDPDK
OVS
Parser Match-Action Pipeline
Compile
Parser Match-Action Pipeline
[1] http://p4.org
P4 is an open-source language.[1]
Easy to express different aspects of a packet processor:- Packet headers and fields- Parser - Actions- Match-Action Tables
P4[1]
KernelDPDK
P4
Parser Match-Action Pipeline
Compile
Parser Match-Action Pipeline
Native OVS Packet Processing Logic
341 lines of code
14,535 lines of code
OVS
Compiler
P4
OVS
parse match action
OVS Executable
header_type tcp_t {
fields {
srcPort : 16;
dstPort : 16;
seqNo : 32;
ackNo : 32;
dataOffset : 4;
res : 4;
window : 16;
checksum : 16;
urgentPtr : 16;
}
}
parser tcp {
extract(tcp);
return ingress;
}
...
header_type tcpv2_t {
fields {
srcPort : 16;
dstPort : 16;
seqNo : 32;
ackNo : 32;
dataOffset : 4;
res : 4;
tcp_flags : 8;
window : 16;
checksum : 16;
urgentPtr : 16;
}
}
parser tcpv2 {
extract(tcpv2);
set_metadata(flow.tcp_flags,
tcpv2.tcp_flags);
return ingress;
}
...
KernelDPDK
OVS
P4
Parser Match-Action Pipeline
Parser Match-Action Pipeline
Performance Overhead?Compile
0
5
10
15
20
25
30
35
40
45
50
64 128 192 256
Thro
ugh
pu
t (G
bp
s)
Packet Size (Bytes)
PISCES v0.1
OVS
Throughput on L2L3-ACL benchmark application
Performance overhead of
~40%
PacketParser
Ingress Match-ActionCache
Match-ActionTables
PacketDeparser
EgressChecksum
VerifyChecksum
Update
CPU Cycles per Packet
Cache Misses
Causes for the Cost on Performance
a. Fully-specified Checksum
b. Parsing unused header fields
and more …
Factors affecting CPU Cycles per Packet
PacketParser
Ingress Match-ActionPipeline
EgressChecksum
VerifyChecksum
Update
Checksum Verify (version, ihl, diffserv, totalLen, identification, flags, fragOffset, ttl, protocol, hdrChecksum, srcAddr, dstAddr)
Checksum Update (version, ihl, diffserv, totalLen, identification, flags, fragOffset, ttl, protocol, hdrChecksum, srcAddr, dstAddr)
PacketParser
IngressDecrement(ttl)
EgressChecksum
VerifyChecksum
Update
Checksum Verify (version, ihl, diffserv, totalLen, identification, flags, fragOffset, ttl, protocol, hdrChecksum, srcAddr, dstAddr)
Incremental Checksum Update (ttl)
Selective Parsing
PacketDeparser
EgressPacketParser
Ingress
Match-ActionPipeline
L2L2 L4
L3
0
2
4
6
8
10
12
14
16
64
Thro
ugh
pu
t (G
bp
s)
Packet Size (Bytes)
PISCES v0.1
incremental Checksum
Header Memory Locality
Selective Parsing
PISCES v1.0
Native OVS
Performance overhead of
< 2%
Throughput on L2L3-ACL benchmark application
Summary
PISCESvSwitch
OVS
P4- Quickly develop and deploy new
packet header format.
- With hardly any performance cost!
Questions?
Learn more and Try PISCES here:
http://pisces.cs.princeton.edu
