Messages in this thread | | | From | Francis Moreau <> | Subject | Re: perf tools miscellaneous questions | Date | Mon, 08 Nov 2010 20:43:48 +0100 |
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Vince Weaver <vweaver1@eecs.utk.edu> writes:
> This is rapidly getting of topic, especially for linux-kernel
Don't think so but feel free to remove LKML from Cc.
[...]
> Most events are poorly documented, if at all. And the Linux kernel > predefined event list is loosely based upon the intel architectural > events, which not every processor has and I've heard from insiders saying > that you should be very careful for the results from those events.
I agree, that's why I try to clarify some events.
Perf tools are cool stuffs, IMHO, but it's pretty hard for me to interpret results. I tried to compare some numbers in my previous posts but I got some 'random' figures for now.
Another example is given below where I'm trying to bench a 2 functions which do the same thing but differently.
$ perf stat -e cache-misses:u,l1d-loads-misses:u,cycles:u -p $(pgrep test) C-c C-c Performance counter stats for process id '30263':
406532 cache-misses 4986030 L1-dcache-load-misses 120247366 cycles
2.482196928 seconds time elapsed
$ perf stat -e cache-misses:u,l1d-loads-misses:u,cycles:u -p $(pgrep test) C-c C-c Performance counter stats for process id '30271':
459683 cache-misses 2513338 L1-dcache-load-misses 159968076 cycles
2.129021265 seconds time elapsed
Which numbers are important here ? cache-misses ? L1-dcache-load-misses ?
I just can say that the first run looks faster.
-- Francis
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