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Overlap Removal and Timing Optimization Studies
Nicole Carlson, Northwestern University
8/8/07Supervisor: Tomasz Bold
2
ATLAS Trigger System
Allotted 40 ms
Allotted 4 s
3
RoI’s in the LVL1 Detector
4
HLT Selection Process
2 most Important Features:
1) Early Rejection Principle
2) Regions of Interest (RoI’s)
RoI’s from LVL1
Chain Signature
Algorithm
TE’s
5
Reason for the Overlap Algorithm
• If one wants a jet + electron in one event from the calorimeter, it is important when looking at the combined signature to make sure they come from different eta/phi
• If two TE’s have exactly the same RoI eta/phi position, then they probably originated from the same cluster
• The chain needs to be stopped (since in reality, both TE’s describe the same physical object)
6
Basic Method
• ComboAlgo to compare 2 or more types• Path:
offline/Trigger/TrigAlgorithms/TrigGenericAlgs/AlgoOverlap.h (NEW PACKAGE!)
• Compare the actual center distance between two RoI’s with a user-defined minimum center distance
• If the actual distance (of the specific TE’s) is smaller, then the chain is stopped
• Otherwise, the chain continues
7
Navigation Structure (w/o features) of 1 Event
Electron and jet overlap
so no TE created
Electron and jet overlap
so no TE createdElectron and jet overlap
so no TE created
8
Extra Features: 1)
• Higher multiplicity Triggers can be handled by this algorithm
• e.g. with jet + electron + tau, the algorithm will compare jet, e; jet, tau; e, tau (within the same event)
• Given 3 TE, if one of the combinations fails (say jet, e), then the whole set will fail and no output TE will be created
9
Extra Features: 2)
• User can specify minimum eta and phi distances instead
• This allows for tighter control along one coordinate
• Algorithm rejects those pairs which have both actual eta and phi distances smaller than the user-defined mins
10
Timing Studies 1: Overhead of timing, monitoring, and caching
• 4 Cases:
• 1) Timing & Validation Enabled
• 2) Timing Disabled/Validation Enabled
• 3) “Online Mode”: Timing & Validation Disabled
• 4) Caching Disabled, Timing & Validation Enabled
11
Results200 t-tbar events LVL2 Total Time in various modes
578.7 463.4 466
1044
0200400600800
10001200140016001800
Timing Enabled Timing Disabled Timing andValidationDisabled
CachingDisabled
Mode
Tim
e (m
s)
200 t-tbar events EF Total Time in various modes
3504 3446 3468
4977
01000200030004000500060007000
Timing Enabled Timing Disabled Timing andValidationDisabled
CachingDisabled
Mode
Tim
e (m
s)
12
Key Points
• Disabling the timers reduces consumption in LVL2 but not in EF
• Disabling monitoring does not seem to have an effect
• Caching reduces the time by approximately a factor of 2
13
Timing Studies 2: Overhead of Framework of Algorithms
• The algorithms take a certain amount of time to reconstruct physical objects
• These are run in a steering framework which schedules them so find this scheduling time
• Determine this time by replacing real algorithms with dummy algorithms which do nothing
14
Results
• Overhead of Framework:
• LVL2: ~10%• EF: ~ 4%
L2 Algorithms Overhead
35.98
331.6
0
100
200
300
400
500
600
Dummy Algorithms Real Algorithms
Test
Tim
e (m
s)
EF Algorithms Overhead
57.5
1568
0
500
1000
1500
2000
2500
Dummy Algorithms Real Algorithms
Test
Tim
e (m
s)
15
Fun Stuffs
16
Thanks
• Tomasz Bold, Till Eifert
• NSF, University of Michigan, CERN Summer Student Programme
• Jeremy Herr
• All the other summer students