linux-kernel - Re: boot tracing

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Date:	Tue, 23 Jul 2013 10:18:56 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Sam Ben <sam.bennn@...il.com>
Cc:	Borislav Petkov <bp@...en8.de>, Robin Holt <holt@....com>,
	Robert Richter <rric@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Nate Zimmer <nzimmer@....com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>, Rob Landley <rob@...dley.net>,
	Mike Travis <travis@....com>,
	Daniel J Blueman <daniel@...ascale-asia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Yinghai Lu <yinghai@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: boot tracing


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

> On 07/12/2013 04:53 PM, Ingo Molnar wrote:
> >* Borislav Petkov <bp@...en8.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
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