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Optimised Memory Transfer & Flow Control for High Speed Networks
- Codito Technologies Pvt. Ltd.
- D Y Patil College of Engineering
Current Trends in High Speed Networks
Total network bandwidth triples every 12 months
CPU Processing power doubles every 18 months
Memory performance increases by 10% every 12 months
Software Challenges in High Speed Networks
Data MovementReasons For Copying.
Copying as a bottleneck.
Checksum
Flow Control AlgorithmLarge Bandwidth Delay Product
Software Requirements Specification
Product FunctionsFramework for Data Copy Elimination
Flow Control Algorithm for Optimal Bandwidth Utilization
User Characteristics
ConstraintsApplications
Max Memory Limit per Process
CPU Speed/Network Speed
Zbuf Framework
Assumptions: Memory is not limited. Hardware Checksumming support would further
enhance our implementation. Application program may reuse the buffer but not
the contents of the buffer. Hence we perform explicit exchange of buffers.
Zbuf Allocator
Zbuf Allocator
Process Aaddress space
zalloczbuf
User Domain
Kernel Domain
Memory
Zbuf Zone
zbuf
User/Kernel sharing of memory !!
Zbuf Zone
Zbuf Allocator
User Domain
Kernel DomainMemory
Maintaining Zbufs In User Space
Zbuf Table
zd(Zbuf Descriptor)
zbuf
Size < MTU
Zbuf Table Zbuf Indirect Table
zbuf
Size > MTU
API Calls
int zalloc(size_t size)
int z_send(int sockfd,int zd,size_t len, int flags )
int z_recv(int sockfd,int zd,size_t len, int flags )
size_t zfread(int zd,size_t size, size_t nmemb, FILE *fp)
size_t zfwrite(int zd, size_t size, size_t nmemb, FILE *fp)
Send Module
User Domain
Kernel Domain
Process Aaddress space
Socket Queue
zbuf
Explicit exchange of buffers !!
zbufz_send
Zbufs are allocated inMTU-sized units.
Check-summing ?
Device Driver Interface
Receive Module
Zbuf Allocator
Zbuf Port Registration !!
Socket Queue
z_recv
User Domain
Kernel Domain
Process Aaddress space
Device Driver Interface
zbufs are grouped together.
zbuf
Flow Control Algorithms for High-Speed Networks
BW-delay product: 1Gb/s WAN * 100 msec RTT = 100Mb
TCP Reno:
Re-convergence to optimal b/w takes a long time !!
Packet-Pair Flow Control
Feedback Based Adaptive Rate Control Scheme.
Estimates n/w state by sending data packets in pairs.
Adapts to changes in n/w state within one RTT.
Assumptions: Network consists of FQ servers.
Routing table updates are infrequent.
Packets are of same size.
Packet Pair Probes
Inter ack spacing estimates bottleneck service rate.
Pipeline depth is determined within one RTT.
Sending rate is modified according to inter ack spacing.
Design Strategy
State MachineStartup
Queue Priming
Normal Transmission
Buffer Management Strategy
Retransmission Strategy
Zbuf Framework Statistics
0 1024 2048 5120 8192 102400
510
15
2025
30
3540
45
5055
60
6570
TCP STATISTICS
Zbuf
Normal
Buffer Size(bytes)
Time (m
icrose
c)
0 1024 2048 5120 8192 10240051015202530354045505560657075
UDP STATISTICS
Zbuf
Normal
Buffer Size(bytes)
Tim
e (m
icro
sec)