Re: [PATCH 3/7 v6] perf/core: Add a callback to perf events

[Frederic Weisbecker <fweisbec@gmail.com>]

On Wed, Nov 18, 2009 at 10:31:09AM +0100, Peter Zijlstra wrote:
> On Wed, 2009-11-18 at 01:18 +0100, Frederic Weisbecker wrote:
> > On Tue, Nov 17, 2009 at 12:28:53PM +0100, Peter Zijlstra wrote:
> > > On Sun, 2009-11-08 at 16:28 +0100, Frederic Weisbecker wrote:
> > > > A simple callback in a perf event can be used for multiple purposes.
> > > > For example it is useful for triggered based events like hardware
> > > > breakpoints that need a callback to dispatch a triggered breakpoint
> > > > event.
> > > > 
> > > > v2: Simplify a bit the callback attribution as suggested by Paul
> > > >     Mackerras
> > > 
> > > Yuck! So we add an opaque callback without semantics nor usage.
> > 
> > 
> > Yeah, this is intended for events that need to be able to trigger
> > events to different channels. In the case of hw-breakpoints, it's
> > either perf buffer, ptrace, etc...
> > 
> > Should I add some comments about it?
> 
> At the very least.. describe its semantics and preferably rename the
> thing.


May be "event_triggered"?

 
> Currently I've no clue what it does and why, your description above
> about multiple channels does not at all help me understand how this
> function pointer is used to make that happen.
> 


We need it for hardware breakpoints because if we register a breakpoint
for perf syscall use, we need to dispatch the event to perf. But if we
register it for ptrace, or any in-kernel uses, we need to dispatch the
event somewhere else and then we need another callback.