[PATCH 7/7] rteval: Warn when all CPUs isolated and loads have no CPUs

Add a warning when all online CPUs are isolated (via isolcpus boot
parameter) and the loads cpulist is empty. This edge case occurs when
a user isolates all CPUs but doesn't explicitly specify where loads
should run, resulting in loads having no CPUs available.

The warning guides users to specify --loads-cpulist explicitly in this
rare configuration.

Example scenario that triggers the warning:
  - Boot parameter: isolcpus=0-15 (all CPUs)
  - Command: rteval --cpusets -d 60s (no explicit CPU lists)
  - Result: Loads default cpulist would be empty

The warning appears as:
  "All CPUs are isolated and loads have no CPUs assigned.
   Specify --loads-cpulist explicitly to choose where loads should run."

Assisted-by: Claude Sonnet 4.5 <[email protected]>
Signed-off-by: John Kacur <[email protected]>
---
 rteval-cmd | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/rteval-cmd b/rteval-cmd
index 37db9e5e2ce2..c48c3d89b82e 100755
--- a/rteval-cmd
+++ b/rteval-cmd
@@ -477,6 +477,15 @@ if __name__ == '__main__':
             tmplist = [cpu for cpu in tmplist if cpu not in housekeeping_cpus]
             msrcfg.cpulist = collapse_cpulist(tmplist)
 
+        # Warn if all CPUs are isolated and loads have no CPUs
+        if not ldcfg.cpulist:
+            isolated_cpus = SysTopology().isolated_cpus()
+            online_cpus = SysTopology().online_cpus()
+            if isolated_cpus and set(isolated_cpus) == set(online_cpus):
+                logger.log(Log.WARN,
+                    "All CPUs are isolated and loads have no CPUs assigned. "
+                    "Specify --loads-cpulist explicitly to choose where loads should run.")
+
         if ldcfg_cpulist_present:
             logger.log(Log.DEBUG, f"loads cpulist: {ldcfg.cpulist}")
         # if --onlyload is specified msrcfg.cpulist is unused
-- 
2.54.0