Re: boot tracing
From: Sam Ben
Date: Sun Jul 14 2013 - 21:39:21 EST
On 07/12/2013 04:53 PM, Ingo Molnar wrote:
* Borislav Petkov <bp@xxxxxxxxx> 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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