Re: [RFC] PyTimechart

[Steven Rostedt]

On Wed, 2010-05-12 at 18:59 +0200, Ingo Molnar wrote:
> * Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> 
> > On Wed, 2010-05-12 at 16:48 +0200, Frederic Weisbecker wrote:
> > > On Wed, May 12, 2010 at 03:37:27PM +0200, Pierre Tardy wrote:
> > 
> > > But we don't yet support trace_printk in perf. May be we could wrap
> > > them in trace events.
> > 
> > Hmm, do we really want to do that?
> > 
> > We really need to get the perf and ftrace trace buffers combined. I 
> > understand why perf chose to do the mmap buffers for the counting, but for 
> > live streaming, it is very inefficient compared to splice.
> 
> The thing is that for a very long time ftrace didnt have splice support and 
> survived just fine. Even today most of the ftrace usage isnt utilizing splice.

Actually, trace-cmd implements the splice interface and is used by
several people. I find myself using trace-cmd 90% of the time that I use
ftrace, specifically because of this speedup.

> 
> Yes, splice might help in some situations but on average it's an independent 
> speedup on the order of magnitude of a few percents, not a 'must have' item.

I'll have start running benchmarks to see what the actual speed up is.
I'm guessing it may be more than a few percent. It allows for zero copy
overhead and reuse of the data page.

-- Steve


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