Re: [PATCH v6] Unified trace buffer

[Steven Rostedt]

On Fri, 26 Sep 2008, Masami Hiramatsu wrote:

> Peter Zijlstra wrote:
> > On Fri, 2008-09-26 at 14:05 -0400, Steven Rostedt wrote:
> >> +static void
> >> +rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned
> >> nr_pages)
> >> +{
> >> +       struct page *page;
> >> +       struct list_head *p;
> >> +       unsigned i;
> >> +
> >> +       atomic_inc(&cpu_buffer->record_disabled);
> > 
> > You probably want synchronize_sched() here (and similar other places) to
> > ensure any active writer on the corresponding cpu is actually stopped.
> 
> Would it really be done in the buffer layer?
> I think it should be done by each tracer, because buffer layer
> can't ensure truly active writers have stopped.
> 

Actually it can ;-)

Since all writes to the buffer at least disable preemption, by issuing a 
synchronize_sched, we can guarantee that after disabling the record, all 
activity will be done.

-- Steve

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