I recently gave a presentation at the local UNIX users group titled Debugging Java performance
problems. The presentation describes various opensource tools and how they can be used to understand what is causing CPU, memory and lock contention issues inside a Java virtual machine. If there are additional tools not discussed in the presentation that you find useful for debugging Java performance problems, please let me know through the comment feature.
Slashdot and other sites had mention of the release of the 2.6.27 Linux kernel today. Some of the new features in the kernel take from here about improved SMP support for the page cache:
The page cache is the place where the kernel keeps in RAM a copy of a file to improve performance by avoiding disk I/O when the data that needs to be read is already on RAM. Each “mapping”, which is the data structure that keeps track of the correspondence between a file and the page cache, is SMP-safe thanks to its own lock. So when different processes in different CPUs access different files, there’s no lock contention, but if they access the same file (shared libraries or shared data files for example), they can hit some contention on that lock. In 2.6.27, thanks to some rules on how the page cache can be used and the usage of RCU, the page cache will be able to do lookups (ie., “read” the page cache) without needing to take the mapping lock, and hence improving scalability. But it will only be noticeable on systems with lots of cpus (page fault speedup of 250x on a 64 way system have been measured).
Hasn’t Solaris been able to successfully scale vertically on 64+ CPU systems since the Solaris 2.5.1 days back on the E10k in 1996 without this type of contention? It also seems like this kernel version brings new enhancements to direct I/O. This also was implemented back in Solaris 6?
Its great that work is being done in the Linux kernel now to allow for vertical scalability, but it just seems to me that these are already mature kernel features that have been around in Solaris for years.
I have been a long time Cowboy Mouth fan, and still remember the first time I saw them play a concert in Delaware. They had an incredible amount of energy, and where one of the few bands I had seen that wanted the crowd involved in every aspect of the show. When I heard they were playing one of the local festivals here in town, I decided to venture out with a few friends to see them.
The show started off like all Cowboy Mouth shows with a ton of energy, and the lead singer (who also plays drums) jamming on drums to get the crowd into the show! I don’t recall the full set list, but the show peaked when they jammed out their classic hit “Jenny Says”! These guys are totally rad, and I can’t wait to see them again in the near future!