Messages in this thread | | | Date | Tue, 27 Mar 2012 11:09:48 -0700 | From | Arun Sharma <> | Subject | Re: [PATCH] perf: Add a new sort order: SORT_INCLUSIVE (v4) |
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On 3/24/12 7:14 PM, Frederic Weisbecker wrote:
>> The other problem in branch stacks/LBR is that they're >> sampled branches. Just because I got a sample with: >> >> a -> b >> b -> c >> >> doesn't necessarily mean that the callchain was a -> b -> c. > > Not sure what you mean. If you have a -> b, b -> c in single > LBR sample it means you got a -> b -> c. >
I was going by Stephane's commit message here:
http://article.gmane.org/gmane.linux.kernel/1236999
> Statistical sampling of taken branch should not be confused > for branch tracing. Not all branches are necessarily captured
Stephane, could you please explain if the 16 filtered branches in LBR are guaranteed to be from a given callchain to the leaf function? My understanding is that it's not.
callchain1: a -> b -> d -> e (sample a->b) callchain2: a -> c -> b -> f (sample b->f)
on PMU interrupt can we end up with:
b -> f <- top of stack a -> b ...
even though a -> b -> f can never happen in the actual program flow?
-Arun
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