Title: Approximate VCCs: A New Characterization of Multimedia Workloads for Systemlevel MpSoC Design
1Approximate VCCs A New Characterization of
Multimedia Workloads for System-level MpSoC
Design
- Speaker Yanhong Liu
- Joint work with
- Samarjit Chakraborty and Wei Tsang Ooi
National University of Singapore
2Introduction
- Portable multimedia devices are widely used, such
as PDAs and mobile phones - Configurable MpSoC platforms are used
- Eclipse, Viper, OMAP, PrimeXsys
- Representative audio/video clips are analyzed
- on-chip buffer sizes, frequency, cache
configurations
3Variability Characterization Curves
- Multimedia streams exhibit high variability
- execution requirements, arrival pattern etc.
- Various kinds of variability should be captured
when analyzing representative clips - The concept of variability characterization
curves (VCCs) was proposed to characterize the
worst-case characteris-tics of various kinds of
variability - Workload curve ?(k)
- execution requirements
- Arrival curve ?(?)
- arrival pattern
- Service curve ?(?)
- computing power
- etc.
4Definition of Workload Curve ?(k)
? ( ?l (k), ?u (k) ) min/max no. of cycles
required to process any k consecutive
stream objects
Sum the cycle numbers within the window, for each
position of the window, and get S
Record the min and max to obtain ? ( ?l(k),
?u(k) ) ?l(k) min S, ?u(k) max S
5Definition of Arrival Curve ?(?)
? ( ?l (?), ?u (?) ) min/max no. of stream
objects that can arrive within any
consecutive time interval of length ?
Sum no. of stream objects within the window, for
each position of the window, and get S
Record the min and max to obtain ? ( ?l(?),
?u(?) ) ?l(?) min S, ?u(?) max S
6Application of VCCs
-
- Using VCCs we can compute
- min buffer size required - on-chip buffer
sizing - bounds on output pattern of the processed stream
- min frequency at which the processor should be
run (using the workload curve) - processor
frequency selection
7 Cycles to Decode a Macroblock
Histogram of cycle demands (maximum 92247)
8Our Work
- Worst cases happen rarely in multimedia
processing - Worst-case load/average-case load can be 10
- Most multimedia applications tolerate that some
data are dropped or miss the playback deadlines - Worst-case analysis using VCCs is overly
pessimistic - To characterize the average-case behaviors of
multimedia workloads, we propose the concept of
approximate VCCs - By taking into account the frequency of
occurrence of certain arrival patterns and
execution demands, and ignoring the very unlikely
cases, we can do better - Resource savings vs. quality degradation
9Approximate VCCs
- The values measured for each position of the
window over a trace are recorded as - An approximate VCC is associated with a parameter
? - Upper curve removing largest ? percent of items
- Lower curve removing smallest ? percent of items
- How to remove?
10Constructing Histogram
occurrence ratio
ri
Cm-1
C0
C1
C2
Cm
11Identify the boundary
occurrence ratio
r2
r1
rm-1
rm
C0
C1
C2
Cm
Cm-1
12Error Analysis
- Resource savings vs. quality degradation
- We analytically obtain upper bound on the errors
associated with different values of e - avoid time-consuming simulation
- Illustrate with two typical system-design cases
- On-chip buffer sizing
- Processor frequency selection
13On-chip Buffer Sizing
- Given a stream, identify if a stream object might
be dropped or not, and then give an upper bound
on the percentage of stream objects that might be
dropped
14Processor Frequency Selection
- Minimum frequency configured for a processor to
sustain the playback rate
workload curve bounds on the execution
requirements of stream objects
- Given a stream, identify if a stream object
misses its deadline or not, and then give an
upper bound on the percentage of stream objects
that might miss deadlines
15Empirical Validation
16Buffer Size vs. Quality(psnr)
Computed buffer sizes for different values of ?
17Percentage of Dropped Macroblocks
Percentage of dropped macroblocks for different
values of ?
18Frequency vs. Quality
of macroblocks missing deadlines
Note suitable frequency selection is related to
playback delay
19Conclusion
- Simulation-based approach is time-consuming
- Worst-case analysis vs. average-case analysis
- We propose the concept of approximate VCCs and
analytically bound degradation in the output
quality - achieve a trade-off between resource savings and
output quality - We bound the number of dropped stream objects for
a stream - extend to bound the number of dropped stream
objects for a class of streams
20thanks!