From 506e64e710ff9573fd2b86686528762b7901b5e4 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Fri, 14 Mar 2025 10:26:56 -0700 Subject: perf: attach/detach PMU specific data The LBR call stack data has to be saved/restored during context switch to fix the shorter LBRs call stacks issue in the system-wide mode. Allocate PMU specific data and attach them to the corresponding task_struct during LBR call stack monitoring. When a LBR call stack event is accounted, the perf_ctx_data for the related tasks will be allocated/attached by attach_perf_ctx_data(). When a LBR call stack event is unaccounted, the perf_ctx_data for related tasks will be detached/freed by detach_perf_ctx_data(). The LBR call stack event could be a per-task event or a system-wide event. - For a per-task event, perf only allocates the perf_ctx_data for the current task. If the allocation fails, perf will error out. - For a system-wide event, perf has to allocate the perf_ctx_data for both the existing tasks and the upcoming tasks. The allocation for the existing tasks is done in perf_event_alloc(). If any allocation fails, perf will error out. The allocation for the new tasks will be done in perf_event_fork(). A global reader/writer semaphore, global_ctx_data_rwsem, is added to address the global race. - The perf_ctx_data only be freed by the last LBR call stack event. The number of the per-task events is tracked by refcount of each task. Since the system-wide events impact all tasks, it's not practical to go through the whole task list to update the refcount for each system-wide event. The number of system-wide events is tracked by a global variable global_ctx_data_ref. Suggested-by: "Peter Zijlstra (Intel)" Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20250314172700.438923-3-kan.liang@linux.intel.com --- include/linux/perf_event.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 75d9b1e93f39..2551170c0d18 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -676,11 +676,12 @@ struct swevent_hlist { #define PERF_ATTACH_GROUP 0x0002 #define PERF_ATTACH_TASK 0x0004 #define PERF_ATTACH_TASK_DATA 0x0008 -#define PERF_ATTACH_ITRACE 0x0010 +#define PERF_ATTACH_GLOBAL_DATA 0x0010 #define PERF_ATTACH_SCHED_CB 0x0020 #define PERF_ATTACH_CHILD 0x0040 #define PERF_ATTACH_EXCLUSIVE 0x0080 #define PERF_ATTACH_CALLCHAIN 0x0100 +#define PERF_ATTACH_ITRACE 0x0200 struct bpf_prog; struct perf_cgroup; -- cgit v1.2.3