r.proj: add thread scaling benchmark script

Add a benchmark that sweeps the nprocs= thread count from 1 to 8 at two
memory caps and plots the time, speedup, and efficiency metrics, following
the r.param.scale benchmark template with grass.benchmark. It builds a source
project and reprojects a generated raster from EPSG:4326 into EPSG:3857 in a
temporary database, so it is self-contained.

Author: krcoder123

raster/r.proj/benchmark/benchmark_r_proj.py

@@ -0,0 +1,135 @@
+"""Benchmarking of r.proj thread scaling
+raster (2D)
+
+This follows the r.param.scale benchmark structure, sweeping raster size at a
+fixed memory and then memory at a fixed raster size, and plotting the time,
+speedup, and efficiency metrics with grass.benchmark. r.proj sweeps its compute
+thread count through the nprocs= option. Each cell generates a source raster in
+an EPSG:4326 project and reprojects it into EPSG:3857 in a temporary database,
+so the script is self-contained. Run it with
+grass --exec python benchmark_r_proj.py or from any GRASS session.
+"""
+
+import os
+import tempfile
+
+from grass.exceptions import CalledModuleError, GrassError
+from grass.pygrass.modules import Module
+import grass.script as gs
+import grass.benchmark as bm
+
+# Baselines held fixed while one dimension is swept.
+BASE_MAPSIZE = 50e6  # cells
+BASE_MEMORY = 300  # MB
+MAPSIZES = [10e6, 50e6, 100e6]
+MEMORIES = [50, 100, 300, 1000]
+METRICS = ["time", "speedup", "efficiency"]
+MAX_NPROCS = 8
+REPEAT = 3
+
+SRC_PROJECT = "src4326"
+DST_PROJECT = "dst3857"
+INPUT = "benchmark_r_proj_reference"
+OUTPUT = "benchmark_r_proj"
+
+
+def main():
+    gisdbase = tempfile.mkdtemp(prefix="bench_r_proj_")
+    gs.create_project(os.path.join(gisdbase, SRC_PROJECT), epsg="4326")
+    gs.create_project(os.path.join(gisdbase, DST_PROJECT), epsg="3857")
+
+    # Sweep raster size at the baseline memory.
+    results = []
+    for mapsize in MAPSIZES:
+        benchmark(
+            gisdbase,
+            size=int(mapsize**0.5),
+            memory=BASE_MEMORY,
+            label=f"r.proj_{int(mapsize / 1e6)}M",
+            results=results,
+        )
+    plot(results, "rastersize")
+
+    # Sweep memory at the baseline raster size.
+    results = []
+    for memory in MEMORIES:
+        benchmark(
+            gisdbase,
+            size=int(BASE_MAPSIZE**0.5),
+            memory=memory,
+            label=f"r.proj_memory_{memory}MB",
+            results=results,
+        )
+    plot(results, "memory")
+
+
+def benchmark(gisdbase, size, memory, label, results):
+    generate_input(gisdbase, size)
+    with gs.setup.init(
+        os.path.join(gisdbase, DST_PROJECT), env=os.environ.copy()
+    ) as session:
+        env = session.env
+        # Output region from r.proj's own suggested bounds for this input.
+        text = gs.read_command(
+            "r.proj",
+            project=SRC_PROJECT,
+            mapset="PERMANENT",
+            dbase=gisdbase,
+            input=INPUT,
+            method="nearest",
+            flags="g",
+            env=env,
+        )
+        region = dict(token.split("=") for token in text.split())
+        gs.run_command("g.region", env=env, **region)
+
+        module = Module(
+            "r.proj",
+            project=SRC_PROJECT,
+            mapset="PERMANENT",
+            dbase=gisdbase,
+            input=INPUT,
+            output=OUTPUT,
+            method="nearest",
+            memory=memory,
+            env_=env,
+            run_=False,
+            overwrite=True,
+        )
+        results.append(
+            bm.benchmark_nprocs(
+                module, label=label, max_nprocs=MAX_NPROCS, repeat=REPEAT
+            )
+        )
+
+
+def generate_input(gisdbase, size):
+    """Generate the size by size source raster in the EPSG:4326 project,
+    mirroring the r.param.scale benchmark by trying r.surf.fractal and falling
+    back to r.random.surface when fractal is unavailable, for example in a build
+    without FFTW."""
+    with gs.setup.init(
+        os.path.join(gisdbase, SRC_PROJECT), env=os.environ.copy()
+    ) as session:
+        env = session.env
+        gs.run_command(
+            "g.region", n=50, s=40, w=-110, e=-90, rows=size, cols=size, env=env
+        )
+        try:
+            Module("r.surf.fractal", output=INPUT, overwrite=True, env_=env)
+        except (CalledModuleError, GrassError):
+            Module("r.random.surface", output=INPUT, overwrite=True, env_=env)
+
+
+def plot(results, sweep):
+    for metric in METRICS:
+        bm.nprocs_plot(
+            results,
+            filename=f"r_proj_{sweep}_{metric}.svg",
+            title=f"r.proj {sweep} {metric}",
+            metric=metric,
+        )
+
+
+if __name__ == "__main__":
+    main()