sched: document profile=sleep requiring CONFIG_SCHEDSTATS

profile=sleep only works if CONFIG_SCHEDSTATS is set. This patch notes
the limitation in Documentation/kernel-parameters.txt and prints a
warning at boot-time if profile=sleep is used without CONFIG_SCHEDSTAT.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 7 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a13d69b2217d..8ae5fac08dfa 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1444,7 +1444,8 @@ and is between 256 and 4096 characters. It is defined in the file
                         Param: "schedule" - profile schedule points.
                         Param: <number> - step/bucket size as a power of 2 for
                                 statistical time based profiling.
-                        Param: "sleep" - profile D-state sleeping (millisecs)
+                        Param: "sleep" - profile D-state sleeping (millisecs).
+                                Requires CONFIG_SCHEDSTATS
                         Param: "kvm" - profile VM exits.
 
         processor.max_cstate=   [HW,ACPI]
diff --git a/kernel/profile.c b/kernel/profile.c
index 631b75c25d7e..5e95330e5120 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -60,6 +60,7 @@ static int __init profile_setup(char * str)
         int par;
 
         if (!strncmp(str, sleepstr, strlen(sleepstr))) {
+#ifdef CONFIG_SCHEDSTATS
                 prof_on = SLEEP_PROFILING;
                 if (str[strlen(sleepstr)] == ',')
                         str += strlen(sleepstr) + 1;
@@ -68,6 +69,10 @@ static int __init profile_setup(char * str)
                 printk(KERN_INFO
                         "kernel sleep profiling enabled (shift: %ld)\n",
                         prof_shift);
+#else
+                printk(KERN_WARNING
+                        "kernel sleep profiling requires CONFIG_SCHEDSTATS\n");
+#endif /* CONFIG_SCHEDSTATS */
         } else if (!strncmp(str, schedstr, strlen(schedstr))) {
                 prof_on = SCHED_PROFILING;
                 if (str[strlen(schedstr)] == ',')