[PATCH v1] perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option

[PATCH v1] perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option

[Ian Rogers]

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.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/evlist.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index eb7c0d7be064..d53f594ace86 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -1562,6 +1562,20 @@ 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->system_wide) {
+		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

Re: [PATCH v1] perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The warning for using the 'sleep' workload incorrectly triggers for valid targeted profiling commands.
- [Low] Missing explicit POSIX `<string.h>` header inclusion for libc string functions.
--

--- Patch [1]: [PATCH v1] perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option ---
commit 2e20acd0f78b6776954ca8e2c6f58698c556aa50
Author: Ian Rogers <irogers@google.com>

perf evlist: Warn when 'sleep' workload is used without system-wide (-a) option

This commit adds a warning to evlist__prepare_workload() when the workload
executable is 'sleep' and system-wide mode is not enabled. This is intended
to catch cases where users forget the '-a' flag and unintentionally only
profile the sleep process itself.

> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index eb7c0d7be064e..d53f594ace86a 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1562,6 +1562,20 @@ 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->system_wide) {

[Severity: Medium]
Does this warning incorrectly trigger when running a targeted profile?

If a user specifies a target (like -p <pid> or -C 0) and uses sleep as the
duration, target->system_wide is false. However, in these targeted modes,
perf correctly monitors the specified target rather than the sleep process,
making the warning spurious.

Should this check instead verify if perf has fallen back to monitoring the
workload itself (for instance, by checking target__none(target))?

> +		const char *cmd = strrchr(argv[0], '/');
> +
> +		if (cmd)
> +			cmd++;
> +		else
> +			cmd = argv[0];
> +
> +		if (!strcmp(cmd, "sleep")) {

[Severity: Low]
This isn't a bug, but should <string.h> be explicitly included in this file
to guarantee musl libc compatibility?

The perf subsystem guidelines require direct, explicit inclusion of POSIX
headers for libc functions like strcmp() and strrchr() to prevent musl
compilation failures. Relying on implicit inclusions can cause builds to
break in environments where headers strictly separate declarations.

> +			ui__warning("workload '%s' specified without the system-wide (-a) option\n",
> +				    cmd);
> +		}
> +	}
> +

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806021038.2291417-1-irogers@google.com?part=1

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

[Ian Rogers]

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

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

[Ian Rogers]

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
>

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

[Namhyung Kim]

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
> 

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

[Namhyung Kim]

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