linux-kernel - Re: boot tracing

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Date:	Mon, 15 Jul 2013 09:38:39 +0800
From:	Sam Ben <sam.bennn@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
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

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.

>
> Just wanted to highlight this usecase, we might eventually want to support
> it.
>
> [ Note that this is different from boot tracing of one or more trace
>    events - but it's a conceptually pretty close cousin. ]
>   
> Thanks,
>
> 	Ingo
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