perf/core: Provide a kernel-internal interface to get to performance counters

There are reasons for kernel code to ask for, and use, performance
counters.
For example, in CPU freq governors this tends to be a good idea, but
there are other examples possible as well of course.

This patch adds the needed bits to do enable this functionality; they
have been tested in an experimental cpufreq driver that I'm working on,
and the changes are all that I needed to access counters properly.

[fweisbec@gmail.com: added pid to perf_event_create_kernel_counter so
that we can profile a particular task too

TODO: Have a better error reporting, don't just return NULL in fail
case.]

v2: Remove the wrong comment about the fact
    perf_event_create_kernel_counter must be called from a kernel
    thread.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: "K.Prasad" <prasad@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jan Kiszka <jan.kiszka@web.de>
Cc: Avi Kivity <avi@redhat.com>
LKML-Reference: <20090925122556.2f8bd939@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
This commit is contained in:
Arjan van de Ven 2009-09-25 12:25:56 +02:00 committed by Frederic Weisbecker
parent 0f8f86c7bd
commit fb0459d75c
2 changed files with 80 additions and 1 deletions

View File

@ -744,6 +744,12 @@ extern int hw_perf_group_sched_in(struct perf_event *group_leader,
struct perf_cpu_context *cpuctx,
struct perf_event_context *ctx, int cpu);
extern void perf_event_update_userpage(struct perf_event *event);
extern int perf_event_release_kernel(struct perf_event *event);
extern struct perf_event *
perf_event_create_kernel_counter(struct perf_event_attr *attr,
int cpu,
pid_t pid);
extern u64 perf_event_read_value(struct perf_event *event);
struct perf_sample_data {
u64 type;

View File

@ -1725,6 +1725,26 @@ static int perf_release(struct inode *inode, struct file *file)
return 0;
}
int perf_event_release_kernel(struct perf_event *event)
{
struct perf_event_context *ctx = event->ctx;
WARN_ON_ONCE(ctx->parent_ctx);
mutex_lock(&ctx->mutex);
perf_event_remove_from_context(event);
mutex_unlock(&ctx->mutex);
mutex_lock(&event->owner->perf_event_mutex);
list_del_init(&event->owner_entry);
mutex_unlock(&event->owner->perf_event_mutex);
put_task_struct(event->owner);
free_event(event);
return 0;
}
EXPORT_SYMBOL_GPL(perf_event_release_kernel);
static int perf_event_read_size(struct perf_event *event)
{
int entry = sizeof(u64); /* value */
@ -1750,7 +1770,7 @@ static int perf_event_read_size(struct perf_event *event)
return size;
}
static u64 perf_event_read_value(struct perf_event *event)
u64 perf_event_read_value(struct perf_event *event)
{
struct perf_event *child;
u64 total = 0;
@ -1761,6 +1781,7 @@ static u64 perf_event_read_value(struct perf_event *event)
return total;
}
EXPORT_SYMBOL_GPL(perf_event_read_value);
static int perf_event_read_entry(struct perf_event *event,
u64 read_format, char __user *buf)
@ -4638,6 +4659,58 @@ err_put_context:
return err;
}
/**
* perf_event_create_kernel_counter
*
* @attr: attributes of the counter to create
* @cpu: cpu in which the counter is bound
* @pid: task to profile
*/
struct perf_event *
perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
pid_t pid)
{
struct perf_event *event;
struct perf_event_context *ctx;
int err;
/*
* Get the target context (task or percpu):
*/
ctx = find_get_context(pid, cpu);
if (IS_ERR(ctx))
return NULL ;
event = perf_event_alloc(attr, cpu, ctx, NULL,
NULL, GFP_KERNEL);
err = PTR_ERR(event);
if (IS_ERR(event))
goto err_put_context;
event->filp = NULL;
WARN_ON_ONCE(ctx->parent_ctx);
mutex_lock(&ctx->mutex);
perf_install_in_context(ctx, event, cpu);
++ctx->generation;
mutex_unlock(&ctx->mutex);
event->owner = current;
get_task_struct(current);
mutex_lock(&current->perf_event_mutex);
list_add_tail(&event->owner_entry, &current->perf_event_list);
mutex_unlock(&current->perf_event_mutex);
return event;
err_put_context:
if (err < 0)
put_ctx(ctx);
return NULL;
}
EXPORT_SYMBOL_GPL(perf_event_create_kernel_counter);
/*
* inherit a event from parent task to child task:
*/