rtla/timerlat: Do not stop user-space if a cpu is offline

If no CPU list is passed, timerlat in user-space will dispatch
one thread per sysconf(_SC_NPROCESSORS_CONF). However, not all
CPU might be available, for instance, if HT is disabled.

Currently, rtla timerlat is stopping the session if an user-space
thread cannot set affinity to a CPU, or if a running user-space
thread is killed. However, this is too restrictive.

So, reduce the error to a debug message, and rtla timerlat run as
long as there is at least one user-space thread alive.

Link: https://lore.kernel.org/lkml/59cf2c882900ab7de91c6ee33b382ac7fa6b4ed0.1694781909.git.bristot@kernel.org

Fixes: cdca4f4 ("rtla/timerlat_top: Add timerlat user-space support")
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>

Author: Daniel Bristot de Oliveira

tools/tracing/rtla/src/timerlat_u.c

@@ -45,7 +45,7 @@ static int timerlat_u_main(int cpu, struct timerlat_u_params *params)
 
 	retval = sched_setaffinity(gettid(), sizeof(set), &set);
 	if (retval == -1) {
-		err_msg("Error setting user thread affinity\n");
+		debug_msg("Error setting user thread affinity %d, is the CPU online?\n", cpu);
 		exit(1);
 	}
 
@@ -193,7 +193,9 @@ void *timerlat_u_dispatcher(void *data)
 					procs_count--;
 				}
 			}
-			break;
+
+			if (!procs_count)
+				break;
 		}
 
 		sleep(1);