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A1Q8 Solution is wrong
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Bojan
Feb 12, 2012, 11:28:09 PM2/12/12
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In the solution, f = M- 1-9/M is not correct.
It should be f = M - N (1 + 9) / M.
This is because draining and filling takes N cycles each time.
It should be f = M - N (1 + 9) / M.
This is because draining and filling takes N cycles each time.
Tatiana
Feb 13, 2012, 1:29:57 PM2/13/12
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Is this question or statement?
Did you check with prof or TA?
Did you check with prof or TA?
Bojan
Feb 13, 2012, 1:56:43 PM2/13/12
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Statement. I did it by hand, and verified with another student.
I did not check with prof or TA.
(with brackets correctly placed)
{M - N( 1 + 9 ) } /M
I did not check with prof or TA.
(with brackets correctly placed)
{M - N( 1 + 9 ) } /M
Bojan
Feb 13, 2012, 1:58:54 PM2/13/12
to
statement, checked it by hand and verified with another student.
did not check with ta or prof.
proper brackets:
f = {M - N (1+ 9)}/M
did not check with ta or prof.
proper brackets:
f = {M - N (1+ 9)}/M
Tatiana
Feb 13, 2012, 2:30:34 PM2/13/12
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The way I understand it is:
f is fraction of instructions that are executed in parallel
M = total # of instr.
s = # of instr. that are executed sequentially
M - s = # of instr. that are executed in parallel
f = (M-s)/M
In class we saw that initial filling and final draining together cause 1
sequential instructions (by applying Amdahl's law).
Also in class we saw that each N-1 cycle stall causes 1 additional
sequential instruction (by Amdahl's law).
9 sequential instr. for 9 stalls and 1 for initial filling and final
draining.
So s = 9+1 = 10
and f = (M-9-1)/M
- Tatiana
f is fraction of instructions that are executed in parallel
M = total # of instr.
s = # of instr. that are executed sequentially
M - s = # of instr. that are executed in parallel
f = (M-s)/M
In class we saw that initial filling and final draining together cause 1
sequential instructions (by applying Amdahl's law).
Also in class we saw that each N-1 cycle stall causes 1 additional
sequential instruction (by Amdahl's law).
9 sequential instr. for 9 stalls and 1 for initial filling and final
draining.
So s = 9+1 = 10
and f = (M-9-1)/M
- Tatiana
Bojan
Feb 13, 2012, 2:58:50 PM2/13/12
to
1 sequential instruction has to go through N stages. hence it takes N
blocks on the niagram.
blocks on the niagram.
Tatiana
Feb 13, 2012, 3:13:11 PM2/13/12
to
Yes, but (M-s)/M is calculated in terms of number of instructions and
not cycles.
M is total number of instructions and s is number of instructions that
are sequential.
Why would you subtract number of cycles stalled from total number of
instructions?
not cycles.
M is total number of instructions and s is number of instructions that
are sequential.
Why would you subtract number of cycles stalled from total number of
instructions?
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