* [PATCH v9] perf evsel: Find process with busy PMUs for EBUSY
[not found] <CAP-5=fVzG-2oJ1gN=s-W+2r58k8P4M-E3r8aP9zJ2aK_w-K9vQ@mail.gmail.com>
@ 2026-09-15 20:49 ` Chun-Tse Shao
2026-09-16 13:57 ` Arnaldo Carvalho de Melo
0 siblings, 1 reply; 2+ messages in thread
From: Chun-Tse Shao @ 2026-09-15 20:49 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo
Cc: Ian Rogers, Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Mark Rutland, Alexander Shishkin, Jiri Olsa, Adrian Hunter,
James Clark, Thomas Falcon, linux-kernel, linux-perf-users,
Chun-Tse Shao
It parses fdinfo with PMU type, comparing with the event which failed to
open, and report the processes causing EBUSY error.
Testing cycles and intel_pt//
$ ./perf stat -e cycles &
[1] 55569
$ ./perf stat -e intel_pt// &
[2] 55683
$ ./perf stat -e intel_pt//
Error:
The PMU intel_pt counters are busy and in use by another process.
Possible processes:
55683 ./perf stat -e intel_pt//
Only perf with intel_pt was reported.
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Chun-Tse Shao <ctshao@google.com>
Assisted-by: Gemini:gemini-3.1-pro-preview
---
v9:
- Rebased onto perf-tools-next
---
tools/perf/util/evsel.c | 69 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 62 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index b44fd880d2d5..f3f5519d0d3d 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -4354,8 +4354,11 @@ static bool find_process(const char *name)
return ret ? false : true;
}
-static int dump_perf_event_processes(char *msg, size_t size)
+static int dump_perf_event_processes(const struct evsel *evsel,
+ char *msg, size_t size)
{
+ const struct perf_event_attr *failed_attr = &evsel->core.attr;
+ u32 target_pmu_type = evsel->pmu ? evsel->pmu->type : UINT32_MAX;
DIR *proc_dir;
struct dirent *proc_entry;
int printed = 0;
@@ -4386,6 +4389,15 @@ static int dump_perf_event_processes(char *msg, size_t size)
continue;
}
while ((fd_entry = readdir(fd_dir)) != NULL) {
+ const char *target_lnk = "anon_inode:[perf_event]";
+ size_t target_lnk_len = sizeof("anon_inode:[perf_event]") - 1;
+ char fdinfo_buf[1024];
+ int fdinfo_fd;
+ ssize_t fdinfo_size;
+ char *line;
+ char *saveptr;
+ u32 perf_event_type = UINT32_MAX;
+ u32 pmu_type = UINT32_MAX;
ssize_t link_size;
if (fd_entry->d_type != DT_LNK)
@@ -4394,12 +4406,51 @@ static int dump_perf_event_processes(char *msg, size_t size)
if (link_size < 0)
continue;
/* Take care as readlink doesn't null terminate the string. */
- if (!strncmp(buf, "anon_inode:[perf_event]", link_size)) {
+ if (link_size != (ssize_t)target_lnk_len ||
+ strncmp(buf, target_lnk, target_lnk_len))
+ continue;
+
+ /* Let's check the PMU type reserved by this process */
+ scnprintf(buf, sizeof(buf), "%s/fdinfo/%s",
+ proc_entry->d_name, fd_entry->d_name);
+ fdinfo_fd = openat(dirfd(proc_dir), buf, O_RDONLY | O_NONBLOCK);
+ if (fdinfo_fd == -1)
+ continue;
+ fdinfo_size = read(fdinfo_fd, fdinfo_buf, sizeof(fdinfo_buf) - 1);
+ close(fdinfo_fd);
+ if (fdinfo_size < 0)
+ continue;
+ fdinfo_buf[fdinfo_size] = '\0';
+
+ line = strtok_r(fdinfo_buf, "\n", &saveptr);
+ while (line) {
+ if (sscanf(line,
+ "perf_event_attr.type:\t%u",
+ &perf_event_type) == 1) {
+ /* continue parsing */
+ } else if (sscanf(line,
+ "pmu_type:\t%u",
+ &pmu_type) == 1) {
+ /* continue parsing */
+ }
+ line = strtok_r(NULL, "\n", &saveptr);
+ }
+
+ /* Report the process which reserves the conflicted PMU. */
+ /* If fdinfo does not contain PMU type, report it too. */
+ if (perf_event_type == failed_attr->type ||
+ pmu_type == failed_attr->type ||
+ (target_pmu_type != UINT32_MAX &&
+ pmu_type == target_pmu_type) ||
+ (perf_event_type == UINT32_MAX &&
+ pmu_type == UINT32_MAX)) {
int cmdline_fd;
ssize_t cmdline_size;
- scnprintf(buf, sizeof(buf), "%s/cmdline", proc_entry->d_name);
- cmdline_fd = openat(dirfd(proc_dir), buf, O_RDONLY);
+ scnprintf(buf, sizeof(buf),
+ "%s/cmdline",
+ proc_entry->d_name);
+ cmdline_fd = openat(dirfd(proc_dir), buf, O_RDONLY | O_NONBLOCK);
if (cmdline_fd == -1)
continue;
cmdline_size = read(cmdline_fd, buf, sizeof(buf) - 1);
@@ -4410,10 +4461,12 @@ static int dump_perf_event_processes(char *msg, size_t size)
for (ssize_t i = 0; i < cmdline_size; i++) {
if (buf[i] == '\0')
buf[i] = ' ';
+ else if (!isprint((unsigned char)buf[i]))
+ buf[i] = '.';
}
-
if (printed == 0)
- printed += scnprintf(msg, size, "Possible processes:\n");
+ printed += scnprintf(msg, size,
+ "Possible processes:\n");
printed += scnprintf(msg + printed, size - printed,
"%s %s\n", proc_entry->d_name, buf);
@@ -4535,7 +4588,9 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
msg, size,
"The PMU %s counters are busy and in use by another process.\n",
evsel->pmu ? evsel->pmu->name : "");
- return printed + dump_perf_event_processes(msg + printed, size - printed);
+ return printed + dump_perf_event_processes(evsel,
+ msg + printed,
+ size - printed);
break;
case EINVAL:
if (evsel->core.attr.sample_type & PERF_SAMPLE_CODE_PAGE_SIZE && perf_missing_features.code_page_size)
--
2.55.0.1032.g73a4cd73de-goog
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v9] perf evsel: Find process with busy PMUs for EBUSY
2026-09-15 20:49 ` [PATCH v9] perf evsel: Find process with busy PMUs for EBUSY Chun-Tse Shao
@ 2026-09-16 13:57 ` Arnaldo Carvalho de Melo
0 siblings, 0 replies; 2+ messages in thread
From: Arnaldo Carvalho de Melo @ 2026-09-16 13:57 UTC (permalink / raw)
To: Chun-Tse Shao
Cc: Ian Rogers, Namhyung Kim, Peter Zijlstra, Ingo Molnar,
Mark Rutland, Alexander Shishkin, Jiri Olsa, Adrian Hunter,
James Clark, Thomas Falcon, linux-kernel, linux-perf-users
On Tue, Sep 15, 2026 at 01:49:51PM -0700, Chun-Tse Shao wrote:
> It parses fdinfo with PMU type, comparing with the event which failed to
> open, and report the processes causing EBUSY error.
>
> Testing cycles and intel_pt//
>
> $ ./perf stat -e cycles &
> [1] 55569
> $ ./perf stat -e intel_pt// &
> [2] 55683
> $ ./perf stat -e intel_pt//
> Error:
> The PMU intel_pt counters are busy and in use by another process.
> Possible processes:
> 55683 ./perf stat -e intel_pt//
>
> Only perf with intel_pt was reported.
I'll apply this after addressing Sashiko's comments about missing
headers for building on musl libc systems, thanks.
- Arnaldo
> Reviewed-by: Ian Rogers <irogers@google.com>
> Signed-off-by: Chun-Tse Shao <ctshao@google.com>
> Assisted-by: Gemini:gemini-3.1-pro-preview
> ---
> v9:
> - Rebased onto perf-tools-next
> ---
> tools/perf/util/evsel.c | 69 ++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 62 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index b44fd880d2d5..f3f5519d0d3d 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -4354,8 +4354,11 @@ static bool find_process(const char *name)
> return ret ? false : true;
> }
>
> -static int dump_perf_event_processes(char *msg, size_t size)
> +static int dump_perf_event_processes(const struct evsel *evsel,
> + char *msg, size_t size)
> {
> + const struct perf_event_attr *failed_attr = &evsel->core.attr;
> + u32 target_pmu_type = evsel->pmu ? evsel->pmu->type : UINT32_MAX;
> DIR *proc_dir;
> struct dirent *proc_entry;
> int printed = 0;
> @@ -4386,6 +4389,15 @@ static int dump_perf_event_processes(char *msg, size_t size)
> continue;
> }
> while ((fd_entry = readdir(fd_dir)) != NULL) {
> + const char *target_lnk = "anon_inode:[perf_event]";
> + size_t target_lnk_len = sizeof("anon_inode:[perf_event]") - 1;
> + char fdinfo_buf[1024];
> + int fdinfo_fd;
> + ssize_t fdinfo_size;
> + char *line;
> + char *saveptr;
> + u32 perf_event_type = UINT32_MAX;
> + u32 pmu_type = UINT32_MAX;
> ssize_t link_size;
>
> if (fd_entry->d_type != DT_LNK)
> @@ -4394,12 +4406,51 @@ static int dump_perf_event_processes(char *msg, size_t size)
> if (link_size < 0)
> continue;
> /* Take care as readlink doesn't null terminate the string. */
> - if (!strncmp(buf, "anon_inode:[perf_event]", link_size)) {
> + if (link_size != (ssize_t)target_lnk_len ||
> + strncmp(buf, target_lnk, target_lnk_len))
> + continue;
> +
> + /* Let's check the PMU type reserved by this process */
> + scnprintf(buf, sizeof(buf), "%s/fdinfo/%s",
> + proc_entry->d_name, fd_entry->d_name);
> + fdinfo_fd = openat(dirfd(proc_dir), buf, O_RDONLY | O_NONBLOCK);
> + if (fdinfo_fd == -1)
> + continue;
> + fdinfo_size = read(fdinfo_fd, fdinfo_buf, sizeof(fdinfo_buf) - 1);
> + close(fdinfo_fd);
> + if (fdinfo_size < 0)
> + continue;
> + fdinfo_buf[fdinfo_size] = '\0';
> +
> + line = strtok_r(fdinfo_buf, "\n", &saveptr);
> + while (line) {
> + if (sscanf(line,
> + "perf_event_attr.type:\t%u",
> + &perf_event_type) == 1) {
> + /* continue parsing */
> + } else if (sscanf(line,
> + "pmu_type:\t%u",
> + &pmu_type) == 1) {
> + /* continue parsing */
> + }
> + line = strtok_r(NULL, "\n", &saveptr);
> + }
> +
> + /* Report the process which reserves the conflicted PMU. */
> + /* If fdinfo does not contain PMU type, report it too. */
> + if (perf_event_type == failed_attr->type ||
> + pmu_type == failed_attr->type ||
> + (target_pmu_type != UINT32_MAX &&
> + pmu_type == target_pmu_type) ||
> + (perf_event_type == UINT32_MAX &&
> + pmu_type == UINT32_MAX)) {
> int cmdline_fd;
> ssize_t cmdline_size;
>
> - scnprintf(buf, sizeof(buf), "%s/cmdline", proc_entry->d_name);
> - cmdline_fd = openat(dirfd(proc_dir), buf, O_RDONLY);
> + scnprintf(buf, sizeof(buf),
> + "%s/cmdline",
> + proc_entry->d_name);
> + cmdline_fd = openat(dirfd(proc_dir), buf, O_RDONLY | O_NONBLOCK);
> if (cmdline_fd == -1)
> continue;
> cmdline_size = read(cmdline_fd, buf, sizeof(buf) - 1);
> @@ -4410,10 +4461,12 @@ static int dump_perf_event_processes(char *msg, size_t size)
> for (ssize_t i = 0; i < cmdline_size; i++) {
> if (buf[i] == '\0')
> buf[i] = ' ';
> + else if (!isprint((unsigned char)buf[i]))
> + buf[i] = '.';
> }
> -
> if (printed == 0)
> - printed += scnprintf(msg, size, "Possible processes:\n");
> + printed += scnprintf(msg, size,
> + "Possible processes:\n");
>
> printed += scnprintf(msg + printed, size - printed,
> "%s %s\n", proc_entry->d_name, buf);
> @@ -4535,7 +4588,9 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
> msg, size,
> "The PMU %s counters are busy and in use by another process.\n",
> evsel->pmu ? evsel->pmu->name : "");
> - return printed + dump_perf_event_processes(msg + printed, size - printed);
> + return printed + dump_perf_event_processes(evsel,
> + msg + printed,
> + size - printed);
> break;
> case EINVAL:
> if (evsel->core.attr.sample_type & PERF_SAMPLE_CODE_PAGE_SIZE && perf_missing_features.code_page_size)
> --
> 2.55.0.1032.g73a4cd73de-goog
^ permalink raw reply [flat|nested] 2+ messages in thread
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[not found] <CAP-5=fVzG-2oJ1gN=s-W+2r58k8P4M-E3r8aP9zJ2aK_w-K9vQ@mail.gmail.com>
2026-09-15 20:49 ` [PATCH v9] perf evsel: Find process with busy PMUs for EBUSY Chun-Tse Shao
2026-09-16 13:57 ` Arnaldo Carvalho de Melo
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