Messages in this thread | | | Date | Fri, 27 May 2011 09:04:35 -0600 | From | David Ahern <> | Subject | Re: perf: h/w counters not counted and no error/info reported to user |
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On 05/27/2011 03:50 AM, Ingo Molnar wrote: > > * David Ahern <dsahern@gmail.com> wrote: > >> By default (tip-perf-core) perf-stat enables a number of H/W counters: >> >> perf stat -- sleep 1 > > did you mean to do 'perf stat -a sleep 1' ?
Adding the -a has its own problems. It blocks reading from fd=0 (stdin); I have to type Ctrl-D to see the results. The FD array gets initialized to 0 and some case is not erroring out or setting the fd.
perf stat -a -- sleep 1
Performance counter stats for 'sleep 1':
2008.600377 task-clock 545 context-switches 31 CPU-migrations 198 page-faults 101,938,898 cycles 140,734,186,560,480 stalled-cycles-frontend 0 stalled-cycles-backend 115,406,129 instructions
26,361,321 branches 1,068,804 branch-misses
1.003842524 seconds time elapsed
The stalled-cycles-frontend is off the chats, but shows a value. Similarly, backed shows 0 versus <not counted>.
> > 'perf stat sleep 1' in itself will only measure that very simple > command - which does not do much.
Simple program for a simple test. I just wanted to know which counters are available for a given processor.
Per your comment and Corey's I tried a program that does some work:
perf stat -- openssl speed aes
Performance counter stats for 'openssl speed aes':
44964.148608 task-clock 4,593 context-switches 48 CPU-migrations 487 page-faults 124,134,470,217 cycles <not counted> stalled-cycles-frontend <not counted> stalled-cycles-backend 319,440,401,206 instructions 6,710,107,937 branches 1,638,412 branch-misses
45.012092601 seconds time elapsed This time I get data for 4 events -- which I did not get with sleep -- but I get <not counted> for the stalled cycles.
How is the <not counted> supposed to be interpreted?
Also, back to the 'perf stat -- sleep 1' example: If I run it with individual -e <event> args I get values -- up to 3. Sure sleep is a simple program, but some counter value comes out. What's magical about 3?
David
> > Thanks, > > Ingo
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