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    Subject[PATCH 1/7 v6] perf/core: Provide a kernel-internal interface to get to performance counters
    Date
    From: Arjan van de Ven <arjan@infradead.org>

    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>
    ---
    include/linux/perf_event.h | 6 +++
    kernel/perf_event.c | 75 +++++++++++++++++++++++++++++++++++++++++++-
    2 files changed, 80 insertions(+), 1 deletions(-)

    diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    index df9d964..fa151d4 100644
    --- a/include/linux/perf_event.h
    +++ b/include/linux/perf_event.h
    @@ -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;
    diff --git a/kernel/perf_event.c b/kernel/perf_event.c
    index 12b5ec3..02d4ff0 100644
    --- a/kernel/perf_event.c
    +++ b/kernel/perf_event.c
    @@ -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:
    */
    --
    1.6.2.3


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