lkml.org 
[lkml]   [2008]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] Performance Counters for Linux, v4

I'm trying to evaluate this new proposal for the kind of workloads I use
performance counters for, and even the simplest tests don't work.

I'm trying to do a simple aggragate count for some benchmarks here using
timec and I'm getting poor results.

Are any of the problems I'm reporting going to be fixed?

In any case, I was testing aggregate counts on a longer running benchmark,
this time equake from the spec2k benchmark suite, still on the q6600.

If I only count retired instructions, I get consistent results:

timec -e 1

119175255369 instructions (events)
119175255561 instructions (events)
119175255383 instructions (events)


however the minute I add another count, say cycles so I can calculate
CPI/IPC the results for instructions are suddenly off by 33%.

Needless to say, perfmon can handle reading both cycles and instructions
at the same time.


timec -e 0, -e 1
91758816320 cycles (events)
79428247907 instructions (events)

91849140396 cycles (events)
79449560742 instructions (events)


It gets worse when trying to look at cache statistics:

timec -e 1 -e 2 -e 3

59611457943 instructions (events)
1872499771 cache references (events)
97471971 cache misses (events)

59601907232 instructions (events)
1871766376 cache references (events)
97435199 cache misses (events)

and so on

timec -e1 -e2 -e3 -e4


47671703285 instructions (events)
1498246999 cache references (events)
77838085 cache misses (events)
3394839360 branches (events)

47666131604 instructions (events)
1497069685 cache references (events)
78065325 cache misses (events)
3393244879 branches (events)



So apparently this performance counter infrastructure will always be
useless for trying to get plain aggregate counts? It's the simplest case
to get right, so it makes me wonder about the design of the rest of the
infrastructure.

Vince


\
 
 \ /
  Last update: 2008-12-16 18:37    [W:0.152 / U:1.328 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site