Multiple parameters
Last updated on 2024-06-04 | Edit this page
Overview
Questions
- “How do I specify multiple parameters?”
- “How do multiple parameters interact?”
Objectives
- Create scaling results for different proportions of parallelizable code.
- Create and compare scalability plots for codes with different amounts of parallel work.
Adding a second parameter
In this episode, we want to vary P, the fraction of
parallel code, as part of our workflow. To do this, we will add a second
entry under global.parameters and remove the definition for
P under env:
YML
(...)
env:
variables:
OUTPUT: amdahl.json
OUTPUT_PATH: ./Episode6
(...)
global.parameters:
TASKS:
values: [2, 4, 8, 16, 32]
label: TASKS.%%
P:
values: [<Insert values>]
label: P.%%How many values do we want to include for P? We need to
have the same number of values listed for all
global.parameters. This means that to run the previous
scaling study with P=.5, and five values for
TASKS, our global parameters section would specify
.5 for P five times:
YML
global.parameters:
TASKS:
values: [2, 4, 8, 16, 32]
label: TASKS.%%
P:
values: [.5, .5, .5, .5, .5]
label: P.%%Let’s say we want to perform the same scaling study for a second
value of P, .99. This means that we’d have to repeat the
same 5 values for TASKS and then provide the second value
of P 5 times:
YML
global.parameters:
TASKS:
values: [2, 4, 8, 16, 32, 2, 4, 8, 16, 32]
label: TASKS.%%
P:
values: [.5, .5, .5, .5, .5, .99, .99, .99, .99, .99]
label: P.%%At this point, our entire YAML file should look something like
YML
description:
name: Amdahl
description: Run a parallel program
batch:
type: slurm
host: ruby # machine
bank: guests # bank
queue: pbatch # partition
reservation: HPCC1B # reservation for this workshop
env:
variables:
OUTPUT: amdahl.json
OUTPUT_PATH: ./Episode6
study:
- name: run-amdahl
description: run in parallel
run:
# Here's where we include our MPI wrapper:
cmd: |
$(LAUNCHER) amdahl --terse -p $(P) >> $(OUTPUT)
nodes: 1
procs: $(TASKS)
walltime: "00:01:30"
- name: plot
description: Create a plot from `amdahl` results
run:
cmd: |
python3 $(SPECROOT)/plot_terse_amdahl_results.py output.jpg $(run-amdahl.workspace)/TASKS.*/amdahl.json
depends: [amdahl_*]
global.parameters:
TASKS:
values: [2, 4, 8, 16, 32, 2, 4, 8, 16, 32]
label: TASKS.%%
P:
values: [.5, .5, .5, .5, .5, .99, .99, .99, .99, .99]
label: P.%%Challenge
Run the workflow above. Do you generate output.jpg? If
not, why not?
If you use the YAML above, your amdahl-run steps should
work, but your plot step will fail. plot’s
failure will be evident both because output.jpg will be
missing from the plot subdirectory and
because the plot.*.err file in the same directory will
contain an error:
OUTPUT
Traceback (most recent call last):
File "plot_terse_amdahl_results.py", line 46, in <module>
process_files(filenames, output=output)
File "plot_terse_amdahl_results.py", line 10, in process_files
with open(filename, 'r') as file:
FileNotFoundError: [Errno 2] No such file or directory: '~/Episode6/Amdahl_20240328-163359/run-amdahl/TASKS.*/amdahl.json'The problem is that the directory path for .json files
has changed. This will be discussed more below!
The trouble with the YAML above is that our output directory
structure changed when we added a second global parameter, but we didn’t
update the directory path specified under plot.
If we look inside the run-amdahl output folder
(identified as $(run-amdahl.workspace) in our workflow
YAML), its subdirectory names now include information about both global
parameters:
OUTPUT
P.0.5.TASKS.16 P.0.5.TASKS.8 P.0.99.TASKS.4
P.0.5.TASKS.2 P.0.99.TASKS.16 P.0.99.TASKS.8
P.0.5.TASKS.32 P.0.99.TASKS.2
P.0.5.TASKS.4 P.0.99.TASKS.32whereas directory path for our .json files is specified
as $(run-amdahl.workspace)/TASKS.*/amdahl.json under the
plot step.
We could get the plot step to work by simply adding a
wildcard, *, in front of TASKS so that the
path to .json files would be
and the definition for plot would be
YML
- name: plot
description: Create a plot from `amdahl` results
run:
cmd: |
python3 $(SPECROOT)/plot_terse_amdahl_results.py output.jpg $(run-amdahl.workspace)/*TASKS.*/amdahl.json
depends: [amdahl_*]This would allow plot to terminate happily and to
produce an output.jpg file, but that image would plot
output from all .json files as a single line, and we
wouldn’t be able to tell which data points corresponded to a parallel
fraction, \(P=0.85\) and which
corresponded to \(P=0.99\).
If we can generate two plots – one for each value of P –
we’ll more clearly be able to see scaling behavior for these two
situations. We can generate two separate plots by calling
python3 plot_terse_amdahl_results.py ... on two sets of
input files – those in the P.0.5.TASKS* subdirectories of
$(run-amdahl.workspace) and those in the
P.0.99.TASKS* subdirectories.
That means we can generate these two plots by inserting the variable
$(P) into the path –
making the definition for plot
YML
- name: plot
description: Create a plot from `amdahl` results
run:
cmd: |
python3 $(SPECROOT)/plot_terse_amdahl_results.py output.jpg $(run-amdahl.workspace)/P.$(P).TASKS.*/amdahl.json
depends: [amdahl_*]Challenge
Modify your workflow as discussed above to generate output plots for two different values of P. Open these plots and verify they are different from each other. How does changing the workflow to generate two separate plots change the directory structure?
(Feel free to use .5 and .99 or to modify to other values of your choosing.)
Your full YAML file should be similar to
YML
description:
name: Amdahl
description: Run a parallel program
batch:
type: slurm
host: ruby # machine
bank: guests # bank
queue: pbatch # partition
reservation: HPCC1B # reservation for this workshop
env:
variables:
OUTPUT: amdahl.json
OUTPUT_PATH: ./Episode6
study:
- name: run-amdahl
description: run in parallel
run:
# Here's where we include our MPI wrapper:
cmd: |
$(LAUNCHER) amdahl --terse -p $(P) >> $(OUTPUT)
nodes: 1
procs: $(TASKS)
walltime: "00:01:30"
- name: plot
description: Create a plot from `amdahl` results
run:
cmd: |
python3 $(SPECROOT)/plot_terse_amdahl_results.py output.jpg $(run-amdahl.workspace)/P.$(P).TASKS.*/amdahl.json
depends: [amdahl_*]
global.parameters:
TASKS:
values: [2, 4, 8, 16, 32, 2, 4, 8, 16, 32]
label: TASKS.%%
P:
values: [.5, .5, .5, .5, .5, .99, .99, .99, .99, .99]
label: P.%%Modifying plot to include $(P) caused this
step to run twice. As a result, two subdirectories under
plot were created – one for each value of P:
OUTPUT
P.0.5 P.0.99Callout
Instead of modifying the path to our amdahl.json files
to $(run-amdahl.workspace)/P.$(P).TASKS.*/amdahl.json, we
could have equivalently updated it to
$(run-amdahl.workspace)/$(P.label).TASKS.*/amdahl.json.
In other words, P.$(P) is equivalent to
$(P.label). Similarly, in Maestro,
TASKS.$(TASKS) is equivalent to
$(TASKS.label). This syntax works for every global
parameter in Maestro.
Key Points
- “Multiple parameters can be defined under
global.parameters.” - “Lists of values for all global parameters must have the same length; the Nth entries in the lists of values for all global parameters are used in a single job.”