Re: [PATCH] perf record: Add snapshot mode support for perf's regular events

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Nov 25, 2015 at 05:44:00PM +0800, Wangnan (F) wrote:
> 
> 
> On 2015/11/25 17:27, Peter Zijlstra wrote:
> >On Tue, Nov 24, 2015 at 10:00:31PM +0800, Yunlong Song wrote:
> >>In our patch, we create and maintain a user space ring buffer to store
> >>perf's tracing info, instead of directly writing to perf.data file as
> >>before. In snapshot mode, only a SIGUSR2 signal can trigger perf to dump
> >>the tracing info currently stored in the user space ring buffer to
> >>perf.data file.
> >I would very much like to first fix the perf overwrite mode: see
> >lkml.kernel.org/r/20151023151205.GW11639@twins.programming.kicks-ass.net
> 
> I think they can be done in parallel. We can first do something with
> tracking events and perf's output file, and wait for kernel level
> overwrite mode fixed, then decide whether to implement perf's own
> ringbuffer.

That seems backwards; why would you ever want to endlessly copy the
events if you're not going to use them?