Messages in this thread | | | Date | Wed, 3 Nov 2010 22:43:13 +0100 | From | Frederic Weisbecker <> | Subject | Re: perf tools miscellaneous questions |
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On Wed, Nov 03, 2010 at 08:28:59PM +0100, Francis Moreau wrote: > Hello, > > I'm trying to use perf-tools and also to learn some internals about > them. So I prefer to ask all of them in one email. > > The first one is about the list of pre-defined events given by > perf-list. I couldn't find any documentations that describes these > events so excuse me if the question is stupid.
Sorry about that. We indeed need to improve a lot the documentation. May be this particular part could come with the future sysfs exposure of the events.
> > What's the difference between 'cpu-clock' and 'task-clock' event ?
cpu-clock is based on the total time spent on the cpu. task-clock is based only on the time spent on the profiled task, so that doesn't count time spent on other tasks, it has a per thread granularity.
(I might be somehow wrong in my explanation).
> > What's exactly the 'cache-misses' event ? does it include both instructions > _and_ data cache misses ? both L1 and L2 caches ? > > I was expecting so but the following command makes me wondering: > > $ perf stat -e cache-misses:u,l1d-loads-misses:u true > Performance counter stats for 'true': > > 763 cache-misses > 874 L1-dcache-load-misses > > 0.000916609 seconds time elapsed > > Here cache-misses < L1-dcache-load-misses.
Dunno, will let others answer.
> The last question is about the source code annotation done by > perf-report. I'm using it to locate the place in my code that generates > the most data cache miss events. I can read this during a perf-report > session: > > [...] > 0.00 : df215: c3 retq > 0.00 : df216: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) > 0.00 : df21d: 00 00 00 > 10.00 : df220: 48 8b 75 00 mov 0x0(%rbp),%rsi > 80.00 : df224: 48 89 df mov %rbx,%rdi > 0.00 : df227: 41 ff d4 callq *%r12 > 0.00 : df22a: 85 c0 test %eax,%eax > [...] > > If I read the output correctly, most of the dcache misses are coming from > 'mov %rbx, %rdi', and AFAIK this intruction can't generate any dcache > miss. What am I missing ?
Perhaps you need pebs to get the very precise location on your event.
perf stat -e cache-misses:up,l1d-loads-misses:up true
I think the more you add 'p', the more precise it is. Like:
perf stat -e cache-misses:uppp,l1d-loads-misses:uppp true
Not sure how much it will accept though :)
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