2005 © switch pert – beyond fat pipes simon leinen
TRANSCRIPT
2005 © SWITCH 2
Contents
• End-to-end performance initiatives and PERT history• Example PERT activities: GN2-PACE and SWITCH• Lessons learned so far• How Grid developers and users can benefit from PERT
2005 © SWITCH 3
End-to-End Performance Initiatives
Motivation• Observation: Backbone improvements not reflected at end users• Frustrations with differentiated-QoS mechanisms
Ideas for improvement• Education (close the “wizard gap”)• Measurement infrastructures
– In the network, e.g. GN2-JRA1– In the hosts, e.g. Web100
• Human support infrastructure → PERT
2005 © SWITCH 4
Example PERT Initiatives: GN2 PERT
GN2 “PACE” (formerly known as “SA3”) PERT• Oriented towards European projects—including Grids• Large virtual team with participants from many NRENs• Weekly “Case Manager” duty, rotating between organisations• http://www.pert.geant2.net/ (still being built)• http://kb.pert.switch.ch/ (Pilot Knowledge Base)
2005 © SWITCH 5
Example PERT Initiatives: SWITCH PERT
• Includes support for performance of the “commodity” Internet• Small team from our NOC/network engineering group
Other NRENs are building PERT groups as wellbut these are the two I’m most familiar with…
2005 © SWITCH 6
DEISAThroughputReduction
Example GN2 PERT Issue• Iperf (single-stream TCP) measurements between the German and
French DEISA sites usually achieve 900 Mb/s.• DEISA traffic uses Premium IP inside the GEANT backbone.• In parallel, there are 2-3 Gb/s throughput tests between Karlsruhe
and CERN, using LBE (Less Than Best Effort) inside GEANT.• Although there shouldn’t be an impact, DEISA measurements drop
to 400 Mb/s during the Karlsruhe/CERN tests.
2005 © SWITCH 7
DEISAThroughputReduction Issue (2)
DEISA Iperf test traffic
Normal DFN-GEANT traffic
2005 © SWITCH 8
DEISAThroughputReduction Issue
Possible Avenues Towards Resolution:• Missing QoS configuration on DFN's router to GEANT• Try TCP variants that fill the pipe more easily (e.g. BIC, FAST)• More measurements (delay/loss/reordering when with bg. traffic?)• Is this a practical problem at all?
2005 © SWITCH 9
Slow access to download.microsoft.com
Example SWITCH PERT Issue• Users at site X observe low download speeds from software
distribution site (30-70 kbps)
2005 © SWITCH 10
Download Issue (2)
• First tests from a test host close to X result in good rates (30-40 Mbps) → probably an issue within site X, right?
$ wget http://download.microsoft.com/.../dotnetfx.exe
Resolving download.microsoft.com... 195.176.255.136, 195.176.255.135
Connecting to download.microsoft.com[195.176.255.136]:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 24,265,736 [application/octet-stream]
100%[====================================>] 24,265,736 4.49M/s ETA 00:00
13:44:22 (3.54 MB/s) - `dotnetfx.exe' saved [24265736/24265736]
2005 © SWITCH 11
Download Issue (3)
• However, subsequent tests reproduce rates similar to what the customer observed.
$ wget http://download.microsoft.com/.../dotnetfx.exe
Resolving download.microsoft.com... 212.162.0.30
Connecting to download.microsoft.com[212.162.0.30]:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 24,265,736 [application/x-msdownload]
12% [===> ] 2,968,483 7.37K/s ETA 51:32
• Further investigation shows that mapping of download.microsoft.com to actual hosts is highly variable, and the performance of the servers mapped to is even more variable.
2005 © SWITCH 12
Download Issue (4)
• Because SWITCH doesn’t entertain business relationships with Microsoft of its content distributors, suggested that our customer complain to Microsoft (of which they are also a customer).
• Although technically a PERT failure, customer seems happy.
2005 © SWITCH 13
Lessons Learned So Far
• It’s hard to establish contacts with the customer• It’s easy to “lose” the customer• Performance expectations are often unclear• Very hard to close an issue
– Lack of criteria for problem resolution
• Should think in terms of bottlenecks rather than “problem locations”
2005 © SWITCH 14
How Grid Community Can Benefit Today
PERT Knowledgebase (http://kb.pert.switch.ch/)• Lots of performance-related information• In the process of being builtContact the PERT in case of performance problems• If it happens when using GEANT/GN2• After other avenues have been explored (campus system and
networking support)• Through your NREN or (for groups such as DEISA) directlyNew: PERT Consultancy Service• Ask PERT for help with future applications/tests (proactive)
2005 © SWITCH 15
How the Grid Community can Help PERT
• Follow the project and provide constructive criticism• Volunteer as GN2 PERT Subject Matter Expert (SME)• Make the concept known within your communities• Bring interesting cases before the PERT
2005 © SWITCH 16