Re: [PATCH v2] perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option

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 <[email protected]>
> ---
>  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
>