Re: [PATCH 1/3] perf: add context field to perf_event

Frederic Weisbecker
2011-06-29T16:08:54Z

On Wed, Jun 29, 2011 at 06:42:35PM +0300, Avi Kivity wrote:
> The perf_event overflow handler does not receive any caller-derived
> argument, so many callers need to resort to looking up the perf_event
> in their local data structure. This is ugly and doesn't scale if a
> single callback services many perf_events.
>
> Fix by adding a context parameter to perf_event_create_kernel_counter()
> (and derived hardware breakpoints APIs) and storing it in the perf_event.
> The field can be accessed from the callback as event->overflow_handler_context.
> All callers are updated.
>
> Signed-off-by: Avi Kivity <avi@redhat.com>

I believe it can micro-optimize ptrace through register_user_hw_breakpoint() because
we could store the index of the breakpoint that way, instead of iterating through 4 slots.

Perhaps it can help in arm too, adding Will in Cc.

But for register_wide_hw_breakpoint, I'm not sure. kgdb is the main user, may be Jason
could find some use of it.

> ---
> arch/arm/kernel/ptrace.c | 3 ++-
> arch/powerpc/kernel/ptrace.c | 2 +-
> arch/sh/kernel/ptrace_32.c | 3 ++-
> arch/x86/kernel/kgdb.c | 2 +-
> arch/x86/kernel/ptrace.c | 3 ++-
> drivers/oprofile/oprofile_perf.c | 2 +-
> include/linux/hw_breakpoint.h | 10 ++++++++--
> include/linux/perf_event.h | 4 +++-
> kernel/events/core.c | 21 +++++++++++++++------
> kernel/events/hw_breakpoint.c | 10 +++++++---
> kernel/watchdog.c | 2 +-
> samples/hw_breakpoint/data_breakpoint.c | 2 +-
> 12 files changed, 44 insertions(+), 20 deletions(-)
>
> diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
> index 9726006..4911c94 100644
> --- a/arch/arm/kernel/ptrace.c
> +++ b/arch/arm/kernel/ptrace.c
> @@ -479,7 +479,8 @@ static struct perf_event *ptrace_hbp_create(struct task_struct *tsk, int type)
> attr.bp_type = type;
> attr.disabled = 1;
>
> - return register_user_hw_breakpoint(&attr, ptrace_hbptriggered, tsk);
> + return register_user_hw_breakpoint(&attr, ptrace_hbptriggered, NULL,
> + tsk);
> }
>
> static int ptrace_gethbpregs(struct task_struct *tsk, long num,
> diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
> index cb22024..5249308 100644
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -973,7 +973,7 @@ int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
> &attr.bp_type);
>
> thread->ptrace_bps[0] = bp = register_user_hw_breakpoint(&attr,
> - ptrace_triggered, task);
> + ptrace_triggered, NULL, task);
> if (IS_ERR(bp)) {
> thread->ptrace_bps[0] = NULL;
> ptrace_put_breakpoints(task);
> diff --git a/arch/sh/kernel/ptrace_32.c b/arch/sh/kernel/ptrace_32.c
> index 3d7b209..930312f 100644
> --- a/arch/sh/kernel/ptrace_32.c
> +++ b/arch/sh/kernel/ptrace_32.c
> @@ -91,7 +91,8 @@ static int set_single_step(struct task_struct *tsk, unsigned long addr)
> attr.bp_len = HW_BREAKPOINT_LEN_2;
> attr.bp_type = HW_BREAKPOINT_R;
>
> - bp = register_user_hw_breakpoint(&attr, ptrace_triggered, tsk);
> + bp = register_user_hw_breakpoint(&attr, ptrace_triggered,
> + NULL, tsk);
> if (IS_ERR(bp))
> return PTR_ERR(bp);
>
> diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
> index 5f9ecff..473ab53 100644
> --- a/arch/x86/kernel/kgdb.c
> +++ b/arch/x86/kernel/kgdb.c
> @@ -638,7 +638,7 @@ void kgdb_arch_late(void)
> for (i = 0; i < HBP_NUM; i++) {
> if (breakinfo[i].pev)
> continue;
> - breakinfo[i].pev = register_wide_hw_breakpoint(&attr, NULL);
> + breakinfo[i].pev = register_wide_hw_breakpoint(&attr, NULL, NULL);
> if (IS_ERR((void * __force)breakinfo[i].pev)) {
> printk(KERN_ERR "kgdb: Could not allocate hw"
> "breakpoints\nDisabling the kernel debugger\n");
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index 807c2a2..28092ae 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -715,7 +715,8 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
> attr.bp_type = HW_BREAKPOINT_W;
> attr.disabled = 1;
>
> - bp = register_user_hw_breakpoint(&attr, ptrace_triggered, tsk);
> + bp = register_user_hw_breakpoint(&attr, ptrace_triggered,
> + NULL, tsk);
>
> /*
> * CHECKME: the previous code returned -EIO if the addr wasn't
> diff --git a/drivers/oprofile/oprofile_perf.c b/drivers/oprofile/oprofile_perf.c
> index 9046f7b..59acf9e 100644
> --- a/drivers/oprofile/oprofile_perf.c
> +++ b/drivers/oprofile/oprofile_perf.c
> @@ -79,7 +79,7 @@ static int op_create_counter(int cpu, int event)
>
> pevent = perf_event_create_kernel_counter(&counter_config[event].attr,
> cpu, NULL,
> - op_overflow_handler);
> + op_overflow_handler, NULL);
>
> if (IS_ERR(pevent))
> return PTR_ERR(pevent);
> diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
> index d1e55fe..6ae9c63 100644
> --- a/include/linux/hw_breakpoint.h
> +++ b/include/linux/hw_breakpoint.h
> @@ -73,6 +73,7 @@ static inline unsigned long hw_breakpoint_len(struct perf_event *bp)
> extern struct perf_event *
> register_user_hw_breakpoint(struct perf_event_attr *attr,
> perf_overflow_handler_t triggered,
> + void *context,
> struct task_struct *tsk);
>
> /* FIXME: only change from the attr, and don't unregister */
> @@ -85,11 +86,13 @@ modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr);
> extern struct perf_event *
> register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
> perf_overflow_handler_t triggered,
> + void *context,
> int cpu);
>
> extern struct perf_event * __percpu *
> register_wide_hw_breakpoint(struct perf_event_attr *attr,
> - perf_overflow_handler_t triggered);
> + perf_overflow_handler_t triggered,
> + void *context);
>
> extern int register_perf_hw_breakpoint(struct perf_event *bp);
> extern int __register_perf_hw_breakpoint(struct perf_event *bp);
> @@ -115,6 +118,7 @@ static inline int __init init_hw_breakpoint(void) { return 0; }
> static inline struct perf_event *
> register_user_hw_breakpoint(struct perf_event_attr *attr,
> perf_overflow_handler_t triggered,
> + void *context,
> struct task_struct *tsk) { return NULL; }
> static inline int
> modify_user_hw_breakpoint(struct perf_event *bp,
> @@ -122,10 +126,12 @@ modify_user_hw_breakpoint(struct perf_event *bp,
> static inline struct perf_event *
> register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
> perf_overflow_handler_t triggered,
> + void *context,
> int cpu) { return NULL; }
> static inline struct perf_event * __percpu *
> register_wide_hw_breakpoint(struct perf_event_attr *attr,
> - perf_overflow_handler_t triggered) { return NULL; }
> + perf_overflow_handler_t triggered,
> + void *context) { return NULL; }
> static inline int
> register_perf_hw_breakpoint(struct perf_event *bp) { return -ENOSYS; }
> static inline int
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index e0786e3..40264b5 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -855,6 +855,7 @@ struct perf_event {
> u64 id;
>
> perf_overflow_handler_t overflow_handler;
> + void *overflow_handler_context;
>
> #ifdef CONFIG_EVENT_TRACING
> struct ftrace_event_call *tp_event;
> @@ -978,7 +979,8 @@ extern struct perf_event *
> perf_event_create_kernel_counter(struct perf_event_attr *attr,
> int cpu,
> struct task_struct *task,
> - perf_overflow_handler_t callback);
> + perf_overflow_handler_t callback,
> + void *context);
> extern u64 perf_event_read_value(struct perf_event *event,
> u64 *enabled, u64 *running);
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 9efe710..6dd4819 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6150,7 +6150,8 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> struct task_struct *task,
> struct perf_event *group_leader,
> struct perf_event *parent_event,
> - perf_overflow_handler_t overflow_handler)
> + perf_overflow_handler_t overflow_handler,
> + void *context)
> {
> struct pmu *pmu;
> struct perf_event *event;
> @@ -6208,10 +6209,13 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> #endif
> }
>
> - if (!overflow_handler && parent_event)
> + if (!overflow_handler && parent_event) {
> overflow_handler = parent_event->overflow_handler;
> + context = parent_event->overflow_handler_context;
> + }
>
> event->overflow_handler = overflow_handler;
> + event->overflow_handler_context = context;
>
> if (attr->disabled)
> event->state = PERF_EVENT_STATE_OFF;
> @@ -6478,7 +6482,8 @@ SYSCALL_DEFINE5(perf_event_open,
> }
> }
>
> - event = perf_event_alloc(&attr, cpu, task, group_leader, NULL, NULL);
> + event = perf_event_alloc(&attr, cpu, task, group_leader, NULL,
> + NULL, NULL);
> if (IS_ERR(event)) {
> err = PTR_ERR(event);
> goto err_task;
> @@ -6663,7 +6668,8 @@ err_fd:
> struct perf_event *
> perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
> struct task_struct *task,
> - perf_overflow_handler_t overflow_handler)
> + perf_overflow_handler_t overflow_handler,
> + void *context)
> {
> struct perf_event_context *ctx;
> struct perf_event *event;
> @@ -6673,7 +6679,8 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
> * Get the target context (task or percpu):
> */
>
> - event = perf_event_alloc(attr, cpu, task, NULL, NULL, overflow_handler);
> + event = perf_event_alloc(attr, cpu, task, NULL, NULL,
> + overflow_handler, context);
> if (IS_ERR(event)) {
> err = PTR_ERR(event);
> goto err;
> @@ -6957,7 +6964,7 @@ inherit_event(struct perf_event *parent_event,
> parent_event->cpu,
> child,
> group_leader, parent_event,
> - NULL);
> + NULL, NULL);
> if (IS_ERR(child_event))
> return child_event;
> get_ctx(child_ctx);
> @@ -6984,6 +6991,8 @@ inherit_event(struct perf_event *parent_event,
>
> child_event->ctx = child_ctx;
> child_event->overflow_handler = parent_event->overflow_handler;
> + child_event->overflow_handler_context
> + = parent_event->overflow_handler_context;
>
> /*
> * Precalculate sample_data sizes
> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> index 086adf2..b7971d6 100644
> --- a/kernel/events/hw_breakpoint.c
> +++ b/kernel/events/hw_breakpoint.c
> @@ -431,9 +431,11 @@ int register_perf_hw_breakpoint(struct perf_event *bp)
> struct perf_event *
> register_user_hw_breakpoint(struct perf_event_attr *attr,
> perf_overflow_handler_t triggered,
> + void *context,
> struct task_struct *tsk)
> {
> - return perf_event_create_kernel_counter(attr, -1, tsk, triggered);
> + return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
> + context);
> }
> EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
>
> @@ -502,7 +504,8 @@ EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
> */
> struct perf_event * __percpu *
> register_wide_hw_breakpoint(struct perf_event_attr *attr,
> - perf_overflow_handler_t triggered)
> + perf_overflow_handler_t triggered,
> + void *context)
> {
> struct perf_event * __percpu *cpu_events, **pevent, *bp;
> long err;
> @@ -515,7 +518,8 @@ register_wide_hw_breakpoint(struct perf_event_attr *attr,
> get_online_cpus();
> for_each_online_cpu(cpu) {
> pevent = per_cpu_ptr(cpu_events, cpu);
> - bp = perf_event_create_kernel_counter(attr, cpu, NULL, triggered);
> + bp = perf_event_create_kernel_counter(attr, cpu, NULL,
> + triggered, context);
>
> *pevent = bp;
>
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 3d0c56a..0aaa41f 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -371,7 +371,7 @@ static int watchdog_nmi_enable(int cpu)
> /* Try to register using hardware perf events */
> wd_attr = &wd_hw_attr;
> wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
> - event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback);
> + event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
> if (!IS_ERR(event)) {
> printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
> goto out_save;
> diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
> index 0636539..2b85831 100644
> --- a/samples/hw_breakpoint/data_breakpoint.c
> +++ b/samples/hw_breakpoint/data_breakpoint.c
> @@ -60,7 +60,7 @@ static int __init hw_break_module_init(void)
> attr.bp_len = HW_BREAKPOINT_LEN_4;
> attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
>
> - sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
> + sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
> if (IS_ERR((void __force *)sample_hbp)) {
> ret = PTR_ERR((void __force *)sample_hbp);
> goto fail;
> --
> 1.7.5.3
>