On Wed, Jul 24, 2013 at 01:54:00PM -0400, Vince Weaver wrote:
> On Tue, 23 Jul 2013, tip-bot for Peter Zijlstra wrote:
>
> > Commit-ID: a5cdd40c9877e9aba704c020fd65d26b5cfecf18
> > Gitweb:
> > http://git.kernel.org/tip/a5cdd40c9877e9aba704c020fd65d26b5cfecf18
> > Author: Peter Zijlstra <[email protected]>
> > AuthorDate: Tue, 16 Jul 2013 17:09:07 +0200
> > Committer: Ingo Molnar <[email protected]>
> > CommitDate: Tue, 23 Jul 2013 12:17:08 +0200
> >
> > perf: Update perf_event_type documentation
> >
> > Due to a discussion with Adrian I had a good look at the perf_event_type
> > record
> > layout and found the documentation to be somewhat unclear.
>
> This code makes a lot of code changes considering it is "updating
> documentation".
>
> Also, will code following this "documentation" be backward compatible?
>
> Meaning, if you have code that depends on the new fields you've added
> and run on older kernels, will you get sane results? Or will the code
> get garbage and/or segfault in the sample_id fields because you read
> past the end of valid data?
I didn't add any fields, this is simply catching up with what was
already there. But yes, this is very much intended to be compatible.
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 5e2bce9..1274114 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -4462,20 +4462,6 @@ void perf_output_sample(struct perf_output_handle
> > *handle,
> > }
> > }
> >
> > - if (!event->attr.watermark) {
> > - int wakeup_events = event->attr.wakeup_events;
> > -
> > - if (wakeup_events) {
> > - struct ring_buffer *rb = handle->rb;
> > - int events = local_inc_return(&rb->events);
> > -
> > - if (events >= wakeup_events) {
> > - local_sub(wakeup_events, &rb->events);
> > - local_inc(&rb->wakeup);
> > - }
> > - }
> > - }
> > -
> > if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
> > if (data->br_stack) {
> > size_t size;
> > @@ -4511,16 +4497,31 @@ void perf_output_sample(struct perf_output_handle
> > *handle,
> > }
> > }
> >
> > - if (sample_type & PERF_SAMPLE_STACK_USER)
> > + if (sample_type & PERF_SAMPLE_STACK_USER) {
> > perf_output_sample_ustack(handle,
> > data->stack_user_size,
> > data->regs_user.regs);
> > + }
> >
> > if (sample_type & PERF_SAMPLE_WEIGHT)
> > perf_output_put(handle, data->weight);
> >
> > if (sample_type & PERF_SAMPLE_DATA_SRC)
> > perf_output_put(handle, data->data_src.val);
> > +
> > + if (!event->attr.watermark) {
> > + int wakeup_events = event->attr.wakeup_events;
> > +
> > + if (wakeup_events) {
> > + struct ring_buffer *rb = handle->rb;
> > + int events = local_inc_return(&rb->events);
> > +
> > + if (events >= wakeup_events) {
> > + local_sub(wakeup_events, &rb->events);
> > + local_inc(&rb->wakeup);
> > + }
> > + }
> > + }
> > }
I suppose you're 'complaining' about these changes? Yeah, maybe I should
have split them up in a separate patch.
I moved the watermark code from somewhere in the middle of actually
doing the output to the end (where it once was) and added a 'missing'
pair of curlies.
I noticed both oddities when looking at the code to verify the output
format which was updated in the other hunks.
It should be a NOP functionality wise.
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