[PATCH 2/7] rteval: Add core sharing validation for CPU isolation

John Kacur
2026-04-21T18:26:40Z

Add validation to detect and warn when CPUs sharing physical cores are
assigned to different workload types (housekeeping, measurement, load).

When SMT/hyperthreading is enabled, CPUs sharing a physical core also
share L1/L2 caches, execution units, TLB, and other core-level resources.
Running different workload types on sibling threads defeats CPU isolation
and can corrupt real-time measurements or create unreproducible results.

Key features:
- Uses CoreSiblings class to detect which CPUs share physical cores
- Only warns when at least one CPU in a pair is isolated (via isolcpus)
- Checks all three workload type combinations:
* Housekeeping vs Measurement
* Housekeeping vs Load
* Measurement vs Load
- Warning format clearly indicates which CPUs are isolated with "(isol)"
marker

Example warning:
Warning: Housekeeping CPU 0 (isol) shares core with measurement CPU 8 (isol)

Implementation:
- coresiblings.py: Add comment explaining SMT-enabled/disabled behavior
- systopology.py: Add validate_core_sharing() function
- rteval-cmd: Call validation after CPU lists are finalized and log warnings

This validation is purely informational - it warns users but does not
prevent execution, allowing users to make informed decisions about their
CPU configurations.

Assisted-by: Claude Sonnet 4.5 <noreply@anthropic.com>
Signed-off-by: John Kacur <jkacur@redhat.com>
---
rteval-cmd | 8 ++++-
rteval/sysinfo/coresiblings.py | 8 ++++-
rteval/systopology.py | 55 ++++++++++++++++++++++++++++++++++
3 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/rteval-cmd b/rteval-cmd
index a903b537c891..f0efb0117726 100755
--- a/rteval-cmd
+++ b/rteval-cmd
@@ -31,7 +31,7 @@ from rteval.modules.loads import LoadModules
from rteval.modules.measurement import MeasurementModules
from rteval import cpupower
from rteval.version import RTEVAL_VERSION
-from rteval.systopology import SysTopology, parse_cpulist_from_config, validate_housekeeping_cpus
+from rteval.systopology import SysTopology, parse_cpulist_from_config, validate_housekeeping_cpus, validate_core_sharing
from rteval.modules.loads.kcompile import ModuleParameters
from rteval.cpulist_utils import CpuList, is_relative, collapse_cpulist

@@ -446,6 +446,12 @@ if __name__ == '__main__':
logger.log(Log.DEBUG, f"measurement cpulist: {msrcfg.cpulist}")
logger.log(Log.DEBUG, f"workdir: {rtevcfg.workdir}")

+ # Validate core sharing between housekeeping, measurement, and load CPUs
+ if housekeeping_cpus or msrcfg_cpus or ldcfg_cpus:
+ core_warnings = validate_core_sharing(housekeeping_cpus, msrcfg_cpus, ldcfg_cpus)
+ for warning in core_warnings:
+ logger.log(Log.WARN, warning)
+
# if --summarize was specified then just parse the XML, print it and exit
if cmd_opts.rteval___summarize:
for xmlfile in cmd_opts.rteval___summarize:
diff --git a/rteval/sysinfo/coresiblings.py b/rteval/sysinfo/coresiblings.py
index 3c97439d0a39..d55a4b699149 100644
--- a/rteval/sysinfo/coresiblings.py
+++ b/rteval/sysinfo/coresiblings.py
@@ -8,7 +8,13 @@ import os
from rteval.cpulist_utils import expand_cpulist

class CoreSiblings:
- """Query CPU core topology to determine which CPUs share physical cores"""
+ """
+ Query CPU core topology to determine which CPUs share physical cores
+
+ Note: This class works correctly whether SMT/hyperthreading is enabled or disabled.
+ When SMT is disabled, each CPU's thread_siblings_list contains only itself,
+ so the class will correctly report that no CPUs share cores.
+ """

def __init__(self, root="/"):
self.sysdir = os.path.join(root, 'sys', 'devices', 'system', 'cpu')
diff --git a/rteval/systopology.py b/rteval/systopology.py
index 5f2bc291f608..0ee81d5c5e36 100644
--- a/rteval/systopology.py
+++ b/rteval/systopology.py
@@ -294,6 +294,61 @@ def parse_cpulist_from_config(cpulist, run_on_isolcpus=False):
return result

+def validate_core_sharing(housekeeping_cpus, measurement_cpus, load_cpus):
+ """
+ Check for CPUs sharing physical cores across different workload types.
+ Warns if isolated CPUs share cores between housekeeping, measurement, and load groups.
+
+ :param housekeeping_cpus: List of housekeeping CPU integers
+ :param measurement_cpus: List of measurement CPU integers
+ :param load_cpus: List of load CPU integers
+ :return: List of warning messages (empty if no issues)
+ """
+ from rteval.sysinfo.coresiblings import CoreSiblings
+
+ warnings = []
+
+ # Get isolated CPUs
+ isolated_cpus = set(SysTopology().isolated_cpus())
+
+ # Create CoreSiblings instance
+ try:
+ cs = CoreSiblings()
+ except Exception:
+ # If we can't read topology, skip validation
+ return warnings
+
+ def check_pair(cpu1, cpu2, type1, type2):
+ """Check if two CPUs share a core and generate warning if at least one is isolated"""
+ if cs.share_core(cpu1, cpu2):
+ cpu1_isol = cpu1 in isolated_cpus
+ cpu2_isol = cpu2 in isolated_cpus
+
+ # Only warn if at least one CPU is isolated
+ if cpu1_isol or cpu2_isol:
+ cpu1_str = f"{type1} CPU {cpu1}{' (isol)' if cpu1_isol else ''}"
+ cpu2_str = f"{type2} CPU {cpu2}{' (isol)' if cpu2_isol else ''}"
+ warnings.append(f"Warning: {cpu1_str} shares core with {cpu2_str}")
+
+ # Check all three combinations
+ # 1. Housekeeping vs Measurement
+ for hk_cpu in housekeeping_cpus:
+ for msr_cpu in measurement_cpus:
+ check_pair(hk_cpu, msr_cpu, "Housekeeping", "measurement")
+
+ # 2. Housekeeping vs Load
+ for hk_cpu in housekeeping_cpus:
+ for ld_cpu in load_cpus:
+ check_pair(hk_cpu, ld_cpu, "Housekeeping", "load")
+
+ # 3. Measurement vs Load
+ for msr_cpu in measurement_cpus:
+ for ld_cpu in load_cpus:
+ check_pair(msr_cpu, ld_cpu, "Measurement", "load")
+
+ return warnings
+
+
if __name__ == "__main__":

def unit_test():
--
2.53.0