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SubjectRe: [PATCH 7/7] uprobes/perf: Avoid uprobe_apply() whenever possible
* Oleg Nesterov <oleg@redhat.com> [2013-02-04 20:03:05]:

> uprobe_perf_open/close call the costly uprobe_apply() every time,
> we can avoid it if:
>
> - "nr_systemwide != 0" is not changed.
>
> - There is another process/thread with the same ->mm.
>
> - copy_proccess() does inherit_event(). dup_mmap() preserves the
> inserted breakpoints.
>
> - event->attr.enable_on_exec == T, we can rely on uprobe_mmap()
> called by exec/mmap paths.
>
> - tp_target is exiting. Only _close() checks PF_EXITING, I don't
> think TRACE_REG_PERF_OPEN can hit the dying task too often.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
> kernel/trace/trace_uprobe.c | 42 ++++++++++++++++++++++++++++++++++++------
> 1 files changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 1114619..e4aab34 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -677,30 +677,60 @@ __uprobe_perf_filter(struct trace_uprobe_filter *filter, struct mm_struct *mm)
> return false;
> }
>
> +static inline bool
> +uprobe_filter_event(struct trace_uprobe *tu, struct perf_event *event)
> +{
> + return __uprobe_perf_filter(&tu->filter, event->hw.tp_target->mm);
> +}
> +
> static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
> {
> + bool done;
> +
> write_lock(&tu->filter.rwlock);
> - if (event->hw.tp_target)
> + if (event->hw.tp_target) {
> + /*
> + * event->parent != NULL means copy_process(), we can avoid
> + * uprobe_apply(). current->mm must be probed and we can rely
> + * on dup_mmap() which preserves the already installed bp's.
> + *
> + * attr.enable_on_exec means that exec/mmap will install the
> + * breakpoints we need.
> + */
> + done = tu->filter.nr_systemwide ||
> + event->parent || event->attr.enable_on_exec ||
> + uprobe_filter_event(tu, event);
> list_add(&event->hw.tp_list, &tu->filter.perf_events);
> - else
> + } else {
> + done = tu->filter.nr_systemwide;
> tu->filter.nr_systemwide++;
> + }
> write_unlock(&tu->filter.rwlock);
>
> - uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> + if (!done)
> + uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
>
> return 0;
> }
>
> static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
> {
> + bool done;
> +
> write_lock(&tu->filter.rwlock);
> - if (event->hw.tp_target)
> + if (event->hw.tp_target) {
> list_del(&event->hw.tp_list);
> - else
> + done = tu->filter.nr_systemwide ||
> + (event->hw.tp_target->flags & PF_EXITING) ||
> + uprobe_filter_event(tu, event);
> + } else {
> tu->filter.nr_systemwide--;
> + done = tu->filter.nr_systemwide;
> + }
> write_unlock(&tu->filter.rwlock);
>
> - uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> + if (!done)
> + uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
>
> return 0;
> }
> --
> 1.5.5.1
>

--
Thanks and Regards
Srikar Dronamraju



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