Wednesday Aug 15, 2007

Comparing analyzer experiments

When performance tuning an application it is really helpful to be able to compare the performance of the current version of the code with an older version. This was one of the motivators for the performance reporting tool spot. spot takes great care to capture information about the system that the code was run on, the flags used to build the application, together with the obvious things like the profile of the application. The tool spot_diff, which is included in the latest release of spot, pulls out the data from multiple experiments and produces a very detailed comparison between them - indicating if, for example, one version had more TLB misses than another version.

However, there are situations where it's necessary to compare two analyzer experiments, and er_xcmp is a tool which does just that.

er_xcmp extracts the time spent in each routine for the input data that is passed to it, and presents this as a list of functions together with the time spent in each function from each data set. er_xcmp handles an arbitrary number of input files, so it's just as happy comparing three profiles as it is two. It's also able to handle data from bit, so comparisons of instruction count as well as user time are possible.

The input formats can be Analyzer experiments, fsummary output from er_print, or output directories from er_html - all three formats get boiled down to the same thing and handled in the same way by the script.

Here's some example output:

% er_xcmp test.1.er test.2.er
    2.8     8.8 <Total>
    1.8     2.6 foo
    1.0     6.2 main
    N/A     N/A _start
About

Darryl Gove is a senior engineer in the Solaris Studio team, working on optimising applications and benchmarks for current and future processors. He is also the author of the books:
Multicore Application Programming
Solaris Application Programming
The Developer's Edge

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