linux-kernel - Re: [patch] Performance Counters for Linux, v4

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Date:	Mon, 15 Dec 2008 16:07:13 -0500 (EST)
From:	Vince Weaver <vince@...ter.net>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...glemail.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	perfctr-devel@...ts.sourceforge.net
Subject: Re: [patch] Performance Counters for Linux, v4

Hello

I'm trying a more complicated benchmark and getting even stranger
results.

This is still on the Q6600 machine

The benchmark does a loop, reading some memory.  It should have
roughly:
    12295 instructions
     4096 memory loads
     4096 branches

perfmon3 is close on all of these stats, and this is consistent
across runs with a small variation (+/- 3 or so).

The timec program returns 0 (!) for all of the stats except
retired instruction count!  And with certain combinations
of counters I get 0 for all counts.  No error messages 
are printed.

Is this expected behavior?

The test program can be had from:
    http://www.csl.cornell.edu/~vince/projects/perf_counter/


Details below:

#
# Perfmon results
#

# First, trying to read all 5 events at once fails, only 4 counters 
# avail

tasse:~/assembly_tests% pfmon -e INSTRUCTIONS_RETIRED,BRANCH_INSTRUCTIONS_RETIRED,L1D_ALL_CACHE_REF,MEM_LOAD_RETIRED:L1D_MISS ./read_test
cannot configure events: set0 events incompatible or too many events

# Cache results are close to expected, L1D looks a little high

tasse:~/assembly_tests% pfmon -e INSTRUCTIONS_RETIRED,L1D_ALL_CACHE_REF,MEM_LOAD_RETIRED:L1D_MISS ./read_test
12299 INSTRUCTIONS_RETIRED
  4164 L1D_ALL_CACHE_REF
     4 MEM_LOAD_RETIRED:L1D_MISS

# Branch results.  Close to what they should be, though a bit higher
#  than expected.

tasse:~/assembly_tests% pfmon -e INSTRUCTIONS_RETIRED,BRANCH_INSTRUCTIONS_RETIRED,MISPREDICTED_BRANCH_RETIRED ./read_test
12299 INSTRUCTIONS_RETIRED
  4102 BRANCH_INSTRUCTIONS_RETIRED
     1 MISPREDICTED_BRANCH_RETIRED


#
# performance counter v4
#

# Including all stats gives no errors, but gives no results
# either


tasse:~/assembly_tests% ./timec -e 0 -e 1 -e 2 -e 3 -e 4 -e 5 ./read_test

  Performance counter stats for './read_test':

              0.716  task clock ticks     (millisecs)

              85049  cycles               (events)
                  0  instructions         (events)
                  0  cache references     (events)
                  0  cache misses         (events)
                  0  branches             (events)
                  0  branch misses        (events)



#
# If I include the cycles count, I consistently get 0 
#   for all counts???

tasse:~/assembly_tests% ./timec -e 0 -e 1 -e 2 -e 3  ./read_test

  Performance counter stats for './read_test':

              0.520  task clock ticks     (millisecs)

              73833  cycles               (events)
                  0  instructions         (events)
                  0  cache references     (events)
                  0  cache misses         (events)

#
# If I drop the cycles count, I get an instruction count
#   with a value 2300 too high (see previous e-mail)
# And really low cache values.

tasse:~/assembly_tests% ./timec -e 1 -e 2 -e 3  ./read_test

  Performance counter stats for './read_test':

              0.723  task clock ticks     (millisecs)

              14644  instructions         (events)
                  8  cache references     (events)
                  0  cache misses         (events)


#
# And the branch stats don't work either
#

tasse:~/assembly_tests% ./timec -e 1 -e 4 -e 5 ./read_test

  Performance counter stats for './read_test':

              0.711  task clock ticks     (millisecs)

              14643  instructions         (events)
                  0  branches             (events)
                  0  branch misses        (events)

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