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perf/x86/lbr: Fix shorter LBRs call stacks for the system-wide mode

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In the system-wide mode, LBR callstacks are shorter in comparison to
the per-process mode.

LBR MSRs are reset during a context switch in the system-wide mode. For
the LBR call stack, the LBRs should be always saved/restored during a
context switch.

Use the space in task_struct to save/restore the LBR call stack data.

For a system-wide event, it's unnecessagy to update the
lbr_callstack_users for each threads. Add a variable in x86_pmu to
indicate whether the system-wide event is active.

Fixes: 76cb2c617f ("perf/x86/intel: Save/restore LBR stack during context switch")
Reported-by: Andi Kleen <ak@linux.intel.com>
Reported-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Debugged-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250314172700.438923-5-kan.liang@linux.intel.com
This commit is contained in:
Kan Liang 2025-03-14 10:26:58 -07:00 committed by Peter Zijlstra
parent d57e94f5b8
commit 3cec9fd035
2 changed files with 40 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
arch/x86/events/intel/lbr.c
View File

@ -422,11 +422,17 @@ static __always_inline bool lbr_is_reset_in_cstate(void *ctx)
return !rdlbr_from(((struct x86_perf_task_context *)ctx)->tos, NULL);
}
static inline bool has_lbr_callstack_users(void *ctx)
{
return task_context_opt(ctx)->lbr_callstack_users ||
x86_pmu.lbr_callstack_users;
}
static void __intel_pmu_lbr_restore(void *ctx)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
if (task_context_opt(ctx)->lbr_callstack_users == 0 ||
if (!has_lbr_callstack_users(ctx) ||
task_context_opt(ctx)->lbr_stack_state == LBR_NONE) {
intel_pmu_lbr_reset();
return;
@ -503,7 +509,7 @@ static void __intel_pmu_lbr_save(void *ctx)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
if (task_context_opt(ctx)->lbr_callstack_users == 0) {
if (!has_lbr_callstack_users(ctx)) {
task_context_opt(ctx)->lbr_stack_state = LBR_NONE;
return;
}
@ -543,6 +549,7 @@ void intel_pmu_lbr_sched_task(struct perf_event_pmu_context *pmu_ctx,
struct task_struct *task, bool sched_in)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct perf_ctx_data *ctx_data;
void *task_ctx;
if (!cpuc->lbr_users)
@ -553,14 +560,18 @@ void intel_pmu_lbr_sched_task(struct perf_event_pmu_context *pmu_ctx,
* the task was scheduled out, restore the stack. Otherwise flush
* the LBR stack.
*/
task_ctx = pmu_ctx ? pmu_ctx->task_ctx_data : NULL;
rcu_read_lock();
ctx_data = rcu_dereference(task->perf_ctx_data);
task_ctx = ctx_data ? ctx_data->data : NULL;
if (task_ctx) {
if (sched_in)
__intel_pmu_lbr_restore(task_ctx);
else
__intel_pmu_lbr_save(task_ctx);
rcu_read_unlock();
return;
}
rcu_read_unlock();
/*
* Since a context switch can flip the address space and LBR entries
@ -589,9 +600,19 @@ void intel_pmu_lbr_add(struct perf_event *event)
cpuc->br_sel = event->hw.branch_reg.reg;
if (branch_user_callstack(cpuc->br_sel) && event->pmu_ctx->task_ctx_data)
task_context_opt(event->pmu_ctx->task_ctx_data)->lbr_callstack_users++;
if (branch_user_callstack(cpuc->br_sel)) {
if (event->attach_state & PERF_ATTACH_TASK) {
struct task_struct *task = event->hw.target;
struct perf_ctx_data *ctx_data;
rcu_read_lock();
ctx_data = rcu_dereference(task->perf_ctx_data);
if (ctx_data)
task_context_opt(ctx_data->data)->lbr_callstack_users++;
rcu_read_unlock();
} else
x86_pmu.lbr_callstack_users++;
}
/*
* Request pmu::sched_task() callback, which will fire inside the
* regular perf event scheduling, so that call will:
@ -665,9 +686,19 @@ void intel_pmu_lbr_del(struct perf_event *event)
if (!x86_pmu.lbr_nr)
return;
if (branch_user_callstack(cpuc->br_sel) &&
event->pmu_ctx->task_ctx_data)
task_context_opt(event->pmu_ctx->task_ctx_data)->lbr_callstack_users--;
if (branch_user_callstack(cpuc->br_sel)) {
if (event->attach_state & PERF_ATTACH_TASK) {
struct task_struct *task = event->hw.target;
struct perf_ctx_data *ctx_data;
rcu_read_lock();
ctx_data = rcu_dereference(task->perf_ctx_data);
if (ctx_data)
task_context_opt(ctx_data->data)->lbr_callstack_users--;
rcu_read_unlock();
} else
x86_pmu.lbr_callstack_users--;
}
if (event->hw.flags & PERF_X86_EVENT_LBR_SELECT)
cpuc->lbr_select = 0;

1
arch/x86/events/perf_event.h
View File

@ -920,6 +920,7 @@ struct x86_pmu {
const int *lbr_sel_map; /* lbr_select mappings */
int *lbr_ctl_map; /* LBR_CTL mappings */
};
u64 lbr_callstack_users; /* lbr callstack system wide users */
bool lbr_double_abort; /* duplicated lbr aborts */
bool lbr_pt_coexist; /* (LBR|BTS) may coexist with PT */