Re: boot tracing

[Ingo Molnar <mingo@kernel.org>]

* Sam Ben <sam.bennn@gmail.com> wrote:

> On 07/12/2013 04:53 PM, Ingo Molnar wrote:
> >* Borislav Petkov <bp@alien8.de> wrote:
> >
> >>On Fri, Jul 12, 2013 at 10:27:56AM +0200, Ingo Molnar wrote:
> >>>Robert Richter and Boris Petkov are working on 'persistent events'
> >>>support for perf, which will eventually allow boot time profiling -
> >>>I'm not sure if the patches and the tooling support is ready enough
> >>>yet for your purposes.
> >>Nope, not yet but we're getting there.
> >>
> >>>Robert, Boris, the following workflow would be pretty intuitive:
> >>>
> >>>  - kernel developer sets boot flag: perf=boot,freq=1khz,size=16MB
> >>What does perf=boot mean? I assume boot tracing.
> >In this case it would mean boot profiling - i.e. a cycles hardware-PMU
> >event collecting into a perf trace buffer as usual.
> >
> >Essentially a 'perf record -a' work-alike, just one that gets activated as
> >early as practical, and which would allow the profiling of memory
> >initialization.
> >
> >Now, one extra complication here is that to be able to profile buddy
> >allocator this persistent event would have to work before the buddy
> >allocator is active :-/ So this sort of profiling would have to use
> >memblock_alloc().
> 
> Could perf=boot be used to sample the performance of memblock subsystem? 
> I think the perf subsystem is too late to be initialized and monitor 
> this.

Yes, that would be a useful facility as well, for things with many events 
were printk is not necessarily practical. Any tracepoint could be 
utilized.

Thanks,

	Ingo