Re: boot tracing

Sam Ben
2013-07-15T01:38:52Z

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.

>
> 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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