Redis IOThreads calculation: Make sure there is at least 1 IO thread per process.

PiperOrigin-RevId: 716396302

Author: p3rf Team

perfkitbenchmarker/linux_benchmarks/redis_memtier_benchmark.py

@@ -76,7 +76,6 @@
     memtier_pipeline: 1
     placement_group_style: none
     redis_aof: False
-    redis_server_io_threads: 0
   vm_groups:
     servers:
       vm_spec: *default_dual_core

perfkitbenchmarker/linux_packages/redis_server.py

@@ -43,6 +43,8 @@ class RedisEvictionPolicy:
     None,
     'Only supported for redis version >= 6, the '
     'number of redis server IO threads to use.',
+    lower_bound=1,
+    upper_bound=128,
 )
 _IO_THREADS_DO_READS = flags.DEFINE_bool(
     'redis_server_io_threads_do_reads',
@@ -157,10 +159,11 @@ def _GetIOThreads(vm) -> int:
     return _IO_THREADS.value
   # Redis docs suggests that i/o threads should not exceed number of cores.
   nthreads_per_core = vm.CheckLsCpu().threads_per_core
+  num_cpus = vm.NumCpusForBenchmark()
   if nthreads_per_core == 1:
-    return vm.NumCpusForBenchmark() - 1
+    return max(num_cpus - 1, 1)
   else:
-    return vm.NumCpusForBenchmark() // 2
+    return num_cpus // 2
 
 
 def _BuildStartCommand(vm, port: int) -> str: