Unformatted text preview: han Bandwidth
• •
• Secure transfers require involvement of the O/S in the
form of software interrupts/exceptions/traps
overhead per transfer
Long messages amortize overhead;
overhead bigger part of short messages
DMAlike transfers: same overhead shared by many
individual data items
Transfers may be delayed until enough data has been
accumulated for a bulk transfer Some material is adapted from D. Culler & D. Patterson (UCB) S. Ziavras How Summarize Suite Performance (1/4)
• Arithmetic average of execution time of all pgms1
– But they vary by 4X in speed, so some would be more important
than others in arithmetic average • Could add a weight per program, but how pick
weight? 2 – Different companies want different weights for their products • Using the arithmetic mean of performances: WRONG
• SPECRatio: Normalize execution times to reference
computer, yielding a ratio proportional to
performance:
time on reference computer
SPECRatio =
time on computer being rated Some material is adapted from D. Culler & D. Patterson (UCB) S. Ziavras Mean Computer Performance
• Similar problems with n computers and 1 program, or 1 computer and n exclusive
execution modes (such as vector, sequential, parallel), or 1 computer and a suite
of n programs • Assume n programs & 1 computer
programs
computer
• 1 Arithmetic mean time of a given computer for a
given set of n programs (ti for program i) T= 1/n Σi=1n ti • 2 Weighted arithm. mean time (fi: weight of program i) T*= Σi=1n fi*ti Some material is adapted from D. Culler & D. Patterson (UCB) S. Ziavras Arithmetic Mean Performance
Arithmetic Mean Performance
• Ri: execution rate for program i, for 1 ≤ i ≤ n
Ri ~ 1/Ti = a R
1
n i • If π ={f i, for i=1,2,...,n} are the program weights
for i=1
are the program weights
– Weighted arithmetic mean execution rate
n R a = ∑ (f i • R i )
* W
WRONG
N R n
∑
i= i =1 It’s proportional to the sum of the inverses of execution
times
times
1/R*...
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 Fall '09
 D. Culler, D. Patterson

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