Date: Tue, 23 Jul 2013 10:18:56 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Sam Ben <sam.bennn@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>, Robin Holt <holt@sgi.com>,
        Robert Richter <rric@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Nate Zimmer <nzimmer@sgi.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>, Rob Landley <rob@landley.net>,
        Mike Travis <travis@sgi.com>,
        Daniel J Blueman <daniel@numascale-asia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>, Yinghai Lu <yinghai@kernel.org>,
        Mel Gorman <mgorman@suse.de>, Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: boot tracing
Message-ID: <20130723081856.GC16088@gmail.com>
References: <1373594635-131067-1-git-send-email-holt@sgi.com>
 <20130712082756.GA4328@gmail.com>
 <20130712084712.GD24008@pd.tnic>
 <20130712085341.GC4328@gmail.com>
 <51E3529F.6070909@gmail.com>
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* 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
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