[PATCH net] selftests: drv-net: limit RPS test CPUs to supported range

[Gal Pressman <gal@nvidia.com>]

The _get_unused_cpus() function can return CPU numbers >= 16, which
exceeds RPS_MAX_CPUS in toeplitz.c. When this happens, the test fails
with a cryptic message:

  # Exception| Traceback (most recent call last):
  # Exception|   File "/tmp/cur/linux/tools/testing/selftests/net/lib/py/ksft.py", line 319, in ksft_run
  # Exception|     func(*args)
  # Exception|   File "/tmp/cur/linux/tools/testing/selftests/drivers/net/hw/toeplitz.py", line 189, in test
  # Exception|     with bkg(" ".join(rx_cmd), ksft_ready=True, exit_wait=True) as rx_proc:
  # Exception|          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  # Exception|   File "/tmp/cur/linux/tools/testing/selftests/net/lib/py/utils.py", line 124, in __init__
  # Exception|     super().__init__(comm, background=True,
  # Exception|   File "/tmp/cur/linux/tools/testing/selftests/net/lib/py/utils.py", line 77, in __init__
  # Exception|     raise Exception("Did not receive ready message")
  # Exception| Exception: Did not receive ready message

Rename _get_unused_cpus() to _get_unused_rps_cpus() and cap the CPU
search range to RPS_MAX_CPUS.

Fixes: 9cf9aa77a1f6 ("selftests: drv-net: hw: convert the Toeplitz test to Python")
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
---
 .../selftests/drivers/net/hw/toeplitz.py        | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/hw/toeplitz.py b/tools/testing/selftests/drivers/net/hw/toeplitz.py
index d288c57894f6..cd7e080e6f84 100755
--- a/tools/testing/selftests/drivers/net/hw/toeplitz.py
+++ b/tools/testing/selftests/drivers/net/hw/toeplitz.py
@@ -19,6 +19,8 @@ from lib.py import ksft_variants, KsftNamedVariant, KsftSkipEx, KsftFailEx
 
 # "define" for the ID of the Toeplitz hash function
 ETH_RSS_HASH_TOP = 1
+# Must match RPS_MAX_CPUS in toeplitz.c
+RPS_MAX_CPUS = 16
 
 
 def _check_rps_and_rfs_not_configured(cfg):
@@ -67,23 +69,24 @@ def _get_irq_cpus(cfg):
     return cpus
 
 
-def _get_unused_cpus(cfg, count=2):
+def _get_unused_rps_cpus(cfg, count=2):
     """
-    Get CPUs that are not used by Rx queues.
-    Returns a list of at least 'count' CPU numbers.
+    Get CPUs that are not used by Rx queues for RPS.
+    Returns a list of at least 'count' CPU numbers within
+    the RPS_MAX_CPUS supported range.
     """
 
     # Get CPUs used by Rx queues
     rx_cpus = set(_get_irq_cpus(cfg))
 
-    # Get total number of CPUs
-    num_cpus = os.cpu_count()
+    # Get total number of CPUs, capped by RPS_MAX_CPUS
+    num_cpus = min(os.cpu_count(), RPS_MAX_CPUS)
 
     # Find unused CPUs
     unused_cpus = [cpu for cpu in range(num_cpus) if cpu not in rx_cpus]
 
     if len(unused_cpus) < count:
-        raise KsftSkipEx(f"Need at {count} CPUs not used by Rx queues, found {len(unused_cpus)}")
+        raise KsftSkipEx(f"Need at least {count} CPUs in range 0..{num_cpus - 1} not used by Rx queues, found {len(unused_cpus)}")
 
     return unused_cpus[:count]
 
@@ -181,7 +184,7 @@ def test(cfg, proto_flag, ipver, grp):
         ksft_pr(f"RSS using CPUs: {irq_cpus}")
     elif grp == "rps":
         # Get CPUs not used by Rx queues and configure them for RPS
-        rps_cpus = _get_unused_cpus(cfg, count=2)
+        rps_cpus = _get_unused_rps_cpus(cfg, count=2)
         rps_mask = _configure_rps(cfg, rps_cpus)
         defer(_configure_rps, cfg, [])
         rx_cmd += ["-r", rps_mask]
-- 
2.52.0