From 86a27811675a415bd351efca1a194a1a94c082dd Mon Sep 17 00:00:00 2001 From: Chun-Tse Shao Date: Tue, 15 Sep 2026 13:49:51 -0700 Subject: [PATCH] perf evsel: Find process with busy PMUs for EBUSY 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 Signed-off-by: Chun-Tse Shao Assisted-by: Gemini:gemini-3.1-pro-preview [ Added a few missing includes as per Sashiko's review ] Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/evsel.c | 72 +++++++++++++++++++++++++++++++++++++---- 1 file changed, 65 insertions(+), 7 deletions(-) diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c index b44fd880d2d5..c663aafa88b2 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -14,9 +14,12 @@ #include "evsel.h" #include +#include #include +#include #include #include +#include #include #include @@ -4354,8 +4357,11 @@ 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 +4392,15 @@ 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 +4409,51 @@ 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 +4464,12 @@ 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 +4591,9 @@ 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)