A common mistake when trying to record system-wide profiles for a given
duration is running commands like 'perf record sleep 1' or 'perf stat
sleep 1' without passing '-a' / '--all-cpus'. When '-a' is omitted, perf
defaults to per-process monitoring of the sleep process itself, which
does not collect system-wide activity and records very few events.

Add a warning in evlist__prepare_workload() when the workload executable
is 'sleep' and system-wide mode is not enabled.

Assisted-by: Antigravity:gemini-3.6-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/evlist.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index eb7c0d7be064..b3dd097fbb2c 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -11,6 +11,7 @@
 #include <inttypes.h>
 #include <signal.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include <fcntl.h>
 #include <linux/bitops.h>
@@ -1562,6 +1563,20 @@ int evlist__prepare_workload(struct evlist *evlist, struct target *target, const
 	int child_ready_pipe[2], go_pipe[2];
 	char bf;
 
+	if (argv && argv[0] && target && target__none(target)) {
+		const char *cmd = strrchr(argv[0], '/');
+
+		if (cmd)
+			cmd++;
+		else
+			cmd = argv[0];
+
+		if (!strcmp(cmd, "sleep")) {
+			ui__warning("workload '%s' specified without the system-wide (-a) option\n",
+				    cmd);
+		}
+	}
+
 	evlist__set_workload_cork_fd(evlist, -1);
 
 	if (pipe(child_ready_pipe) < 0) {
-- 
2.55.0.629.g250fe7f194-goog

On Wed, 05 Aug 2026 21:14:14 -0700, Ian Rogers wrote:
> A common mistake when trying to record system-wide profiles for a given
> duration is running commands like 'perf record sleep 1' or 'perf stat
> sleep 1' without passing '-a' / '--all-cpus'. When '-a' is omitted, perf
> defaults to per-process monitoring of the sleep process itself, which
> does not collect system-wide activity and records very few events.
> 
> Add a warning in evlist__prepare_workload() when the workload executable
> is 'sleep' and system-wide mode is not enabled.
> 
> [...]
Applied to perf-tools-next, thanks!

Best regards,
Namhyung

On Wed, Aug 05, 2026 at 09:14:14PM -0700, Ian Rogers wrote:
> A common mistake when trying to record system-wide profiles for a given
> duration is running commands like 'perf record sleep 1' or 'perf stat
> sleep 1' without passing '-a' / '--all-cpus'. When '-a' is omitted, perf
> defaults to per-process monitoring of the sleep process itself, which
> does not collect system-wide activity and records very few events.
> 
> Add a warning in evlist__prepare_workload() when the workload executable
> is 'sleep' and system-wide mode is not enabled.
> 
> Assisted-by: Antigravity:gemini-3.6-flash
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/evlist.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index eb7c0d7be064..b3dd097fbb2c 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -11,6 +11,7 @@
>  #include <inttypes.h>
>  #include <signal.h>
>  #include <stdlib.h>
> +#include <string.h>
>  
>  #include <fcntl.h>
>  #include <linux/bitops.h>
> @@ -1562,6 +1563,20 @@ int evlist__prepare_workload(struct evlist *evlist, struct target *target, const
>  	int child_ready_pipe[2], go_pipe[2];
>  	char bf;
>  
> +	if (argv && argv[0] && target && target__none(target)) {

As I read the code, argv and target should be provided.  So the
condition simply can be target__none().  I'll make the change.


> +		const char *cmd = strrchr(argv[0], '/');
> +
> +		if (cmd)
> +			cmd++;
> +		else
> +			cmd = argv[0];
> +
> +		if (!strcmp(cmd, "sleep")) {
> +			ui__warning("workload '%s' specified without the system-wide (-a) option\n",
> +				    cmd);

Now it's not just the system-wide option, but I guess it's most likey
what users want.  I hope this would improve UX of the tool a bit. :)

Thanks,
Namhyung


> +		}
> +	}
> +
>  	evlist__set_workload_cork_fd(evlist, -1);
>  
>  	if (pipe(child_ready_pipe) < 0) {
> -- 
> 2.55.0.629.g250fe7f194-goog
>

On Wed, Aug 5, 2026 at 9:14 PM Ian Rogers <irogers@google.com> wrote:
>
> A common mistake when trying to record system-wide profiles for a given
> duration is running commands like 'perf record sleep 1' or 'perf stat
> sleep 1' without passing '-a' / '--all-cpus'. When '-a' is omitted, perf
> defaults to per-process monitoring of the sleep process itself, which
> does not collect system-wide activity and records very few events.
>
> Add a warning in evlist__prepare_workload() when the workload executable
> is 'sleep' and system-wide mode is not enabled.
>
> Assisted-by: Antigravity:gemini-3.6-flash
> Signed-off-by: Ian Rogers <irogers@google.com>

Ping.

Thanks,
Ian

> ---
>  tools/perf/util/evlist.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index eb7c0d7be064..b3dd097fbb2c 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -11,6 +11,7 @@
>  #include <inttypes.h>
>  #include <signal.h>
>  #include <stdlib.h>
> +#include <string.h>
>
>  #include <fcntl.h>
>  #include <linux/bitops.h>
> @@ -1562,6 +1563,20 @@ int evlist__prepare_workload(struct evlist *evlist, struct target *target, const
>         int child_ready_pipe[2], go_pipe[2];
>         char bf;
>
> +       if (argv && argv[0] && target && target__none(target)) {
> +               const char *cmd = strrchr(argv[0], '/');
> +
> +               if (cmd)
> +                       cmd++;
> +               else
> +                       cmd = argv[0];
> +
> +               if (!strcmp(cmd, "sleep")) {
> +                       ui__warning("workload '%s' specified without the system-wide (-a) option\n",
> +                                   cmd);
> +               }
> +       }
> +
>         evlist__set_workload_cork_fd(evlist, -1);
>
>         if (pipe(child_ready_pipe) < 0) {
> --
> 2.55.0.629.g250fe7f194-goog
>