diff --git a/benchmark/benchmark.py b/benchmark/benchmark.py
index 9ec932e5d..0a17218db 100644
--- a/benchmark/benchmark.py
+++ b/benchmark/benchmark.py
@@ -59,7 +59,7 @@ def __exit__(
             self.foutput.close()
 
     @contextlib.contextmanager
-    def set_env(self, *env_varss: dict[str, str] | None) -> Iterator[None]:
+    def set_env(self, *env_varss: Env_VarsType) -> Iterator[None]:
         """Set environment variables.
 
         All the arguments are dicts of name:value, or None.  All are applied
@@ -116,12 +116,13 @@ def run_command(self, cmd: str) -> str:
         return output.strip()
 
 
-def rmrf(path: Path) -> None:
+def remake(path: Path) -> None:
     """
-    Remove a directory tree.  It's OK if it doesn't exist.
+    Remove a directory tree and recreate it.  It's OK if it doesn't exist.
     """
     if path.exists():
         shutil.rmtree(path)
+    path.mkdir(parents=True)
 
 
 @contextlib.contextmanager
@@ -204,8 +205,9 @@ def shell(self) -> ShellSession:
 
     def make_dir(self) -> None:
         self.dir = Path(f"work_{self.slug}")
-        if self.dir.exists():
-            rmrf(self.dir)
+        remake(self.dir)
+        self.tmpdir = Path(f"tmp_{self.slug}").resolve()
+        remake(self.tmpdir)
 
     def get_source(self, shell: ShellSession, retries: int = 5) -> None:
         """Get the source of the project."""
@@ -277,11 +279,18 @@ def run_with_coverage(self, env: Env, cov_ver: Coverage) -> float:
 class ToxProject(ProjectToTest):
     """A project using tox to run the test suite."""
 
+    ALLOWABLE_ENV_VARS = [
+        "COVERAGE_DEBUG",
+        "COVERAGE_CORE",
+        "COVERAGE_FORCE_CONFIG",
+        "PATH",
+        "TMPDIR",
+    ]
+
     env_vars: Env_VarsType = {
         **(ProjectToTest.env_vars or {}),
         # Allow some environment variables into the tox execution.
-        "TOX_OVERRIDE": "testenv.pass_env+=COVERAGE_DEBUG,COVERAGE_CORE,COVERAGE_FORCE_CONFIG",
-        "COVERAGE_DEBUG": "config,sys",
+        "TOX_OVERRIDE": "testenv.pass_env+=" + ",".join(ALLOWABLE_ENV_VARS),
     }
 
     def prep_environment(self, env: Env) -> None:
@@ -423,22 +432,19 @@ def __init__(self, more_pytest_args: str = ""):
 
     def prep_environment(self, env: Env) -> None:
         env.shell.run_command(f"{env.python} -m pip install tox")
-        Path("/tmp/operator_tmp").mkdir(exist_ok=True)
         env.shell.run_command(f"{env.python} -m tox -e unit --notest")
         env.shell.run_command(f"{env.python} -m tox -e unitnocov --notest")
 
     def run_no_coverage(self, env: Env) -> float:
         env.shell.run_command(
-            f"TMPDIR=/tmp/operator_tmp {env.python} -m tox -e unitnocov --skip-pkg-install"
-            + f" -- {self.more_pytest_args}"
+            f"{env.python} -m tox -e unitnocov --skip-pkg-install -- {self.more_pytest_args}"
         )
         return env.shell.last_duration
 
     def run_with_coverage(self, env: Env, cov_ver: Coverage) -> float:
         env.shell.run_command(f"{env.python} -m pip install {cov_ver.pip_args}")
         env.shell.run_command(
-            f"TMPDIR=/tmp/operator_tmp {env.python} -m tox -e unit --skip-pkg-install"
-            + f" -- {self.more_pytest_args}"
+            f"{env.python} -m tox -e unit --skip-pkg-install -- {self.more_pytest_args}"
         )
         duration = env.shell.last_duration
         report = env.shell.run_command(f"{env.python} -m coverage report --precision=6")
@@ -848,18 +854,17 @@ def __init__(
         py_versions: list[PyVersion],
         cov_versions: list[Coverage],
         projects: list[ProjectToTest],
-        results_file: str = "results.json",
+        results_file: Path = Path("results.json"),
         load: bool = False,
-        cwd: str = "",
     ):
         self.py_versions = py_versions
         self.cov_versions = cov_versions
         self.projects = projects
-        self.results_file = Path(cwd) / Path(results_file)
-        self.result_data: dict[ResultKey, list[float]] = (
-            self.load_results() if load else {}
-        )
+        self.results_file = results_file
+        self.result_data: dict[ResultKey, list[float]] = {}
         self.summary_data: dict[ResultKey, float] = {}
+        if load:
+            self.result_data = self.load_results()
 
     def save_results(self) -> None:
         """Save current results to the JSON file."""
@@ -933,8 +938,13 @@ def run(self, num_runs: int = 3) -> None:
                 )
                 print(banner)
                 env.shell.print_banner(banner)
+                env_vars = [
+                    proj.env_vars,
+                    cov_ver.env_vars,
+                    {"TMPDIR": str(proj.tmpdir)},
+                ]
                 with change_dir(proj.dir):
-                    with env.shell.set_env(proj.env_vars, cov_ver.env_vars):
+                    with env.shell.set_env(*env_vars):
                         try:
                             if cov_ver.pip_args is None:
                                 dur = proj.run_no_coverage(env)
@@ -1056,16 +1066,16 @@ def run_experiment(
         )
 
     print(f"Removing and re-making {PERF_DIR}")
-    rmrf(PERF_DIR)
+    remake(PERF_DIR)
 
-    cwd = str(Path.cwd())
+    results_file = Path("results.json").resolve()
     with change_dir(PERF_DIR):
         exp = Experiment(
             py_versions=py_versions,
             cov_versions=cov_versions,
             projects=projects,
+            results_file=results_file,
             load=load,
-            cwd=cwd,
         )
         exp.run(num_runs=int(num_runs))
         exp.show_results(rows=rows, column=column, ratios=ratios)