This summer, I read a great article +"coz: +This Is the Profiler You're Looking For" in USENIX ;login: about +how to profile multi-threaded programs. It presented a system for +profiling software by running experiences in the running program, +testing how run time performance is affected by "speeding up" parts of +the code to various degrees compared to a normal run. It does this by +slowing down parallel threads while the "faster up" code is running +and measure how this affect processing time. The processing time is +measured using probes inserted into the code, either using progress +counters (COZ_PROGRESS) or as latency meters (COZ_BEGIN/COZ_END). It +can also measure unmodified code by measuring complete the program +runtime and running the program several times instead.
+ +The project and presentation was so inspiring that I would like to +get the system into Debian. I +created +a WNPP request for it and contacted upstream to try to make the +system ready for Debian by sending patches. The build process need to +be changed a bit to avoid running 'git clone' to get dependencies, and +to include the JavaScript web page used to visualize the collected +profiling information included in the source package. +But I expect that should work out fairly soon.
+ +The way the system work is fairly simple. To run an coz experiment +on a binary with debug symbols available, start the program like this: + +
+ ++coz run --- program-to-run +
This will create a text file profile.coz with the instrumentation +information. To show what part of the code affect the performance +most, use a web browser and either point it to +http://plasma-umass.github.io/coz/ +or use the copy from git (in the gh-pages branch). Check out this web +site to have a look at several example profiling runs and get an idea what the end result from the profile runs look like. To make the +profiling more useful you include <coz.h> and insert the +COZ_PROGRESS or COZ_BEGIN and COZ_END at appropriate places in the +code, rebuild and run the profiler. This allow coz to do more +targeted experiments.
+ +A video published by ACM +presenting the +Coz profiler is available from Youtube. There is also a paper +from the 25th Symposium on Operating Systems Principles available +titled +Coz: +finding code that counts with causal profiling.
+ +The source code +for Coz is available from github. It will only build with clang +because it uses a +C++ +feature missing in GCC, but I've submitted +a patch to solve +it and hope it will be included in the upstream source soon.
+ +Please get in touch if you, like me, would like to see this piece +of software in Debian. I would very much like some help with the +packaging effort, as I lack the in depth knowledge on how to package +C++ libraries.
+ +