Re: [PATCH 0/4] perf tools: Persistent events, changes for perf tool integration

[Ingo Molnar <mingo@kernel.org>]

* Robert Richter <rric@kernel.org> wrote:

> From: Robert Richter <robert.richter@calxeda.com>
> 
> This patch set contains userland changes necessary for out-of-the-box
> support of persistent events. These patches are follow on patches of
> the kernel patches I sent out today:
> 
>  [PATCH 00/16] perf, persistent: Kernel updates for perf tool integration
> 
> Persistent events are always enabled kernel events. Buffers are mapped
> readonly and multiple users are allowed. The persistent event flag of
> the event attribute must be set to specify such an event.
> 
> The following changes to perf tools are necessary to support
> persistent events. A way is needed to specify sysfs entries to set
> event flags. For this a new syntax 'attr<num>' was added to the event
> parser, see patch #3. We also need to change perf tools to mmap
> persistent event buffers readonly.

Nice progress - one fundamental thing I'm missing from this series is 
actual everyday utility: it would be nice if it was easy to just create a 
persistent event of any sort and then use it.

For example I might want to instrument a global aspect of the system: 
fork()s performed (-e sched:sched_process_fork).

For that I'd like to create a persistent event that just keeps running, 
and to which I can occasionally attach to read-only to see what's going on 
and maybe attach to it read-write to drain the trace entries. I.e. 
basically a global trace buffer. How do I achieve that with this new 
tooling?

Thanks,

	Ingo