Stories about: Semaphore

The AIM benchmark attempts to measure system throughput by running a large number of tasks (perhaps thousands of them), each of which is exercising some part of the kernel. Yanmin Zhang reported that his AIM results got about 40% worse under the 2.6.26-rc1 kernel. He took the trouble to bisect the problem; the guilty patch turned out to be the generic semaphores code. Reverting that patch made the performance regression go away - at the cost of restoring over 7,000 lines of old, unlamented code. The thought of bringing back the previous semaphore implementation was enough to inspire a few people to look more deeply at the problem.

Linux enthusiasts like to point out just how scalable the system is; Linux runs on everything from pocket-size devices to supercomputers with several thousand processors. What they talk about a little bit less is that, at the high end, the true scalability of the system is limited by the sort of workload which is run. CPU-intensive scientific computing tasks can make good use of very large systems, but database-heavy workloads do not scale nearly as well. There is a lot of interest in making big database systems work better, but it has been a challenging task. Nick Piggin appears to have come up with a logical next step in that direction, though, with a relatively straightforward set of core memory management changes.

Throughout the ages Homo sapiens have developed many excellent ways to communicate. As to which ones are superior, it's difficult to say. All can be measured against certain criteria. A good communications system should be easy to use, clear, secure, scalable and accessible. It should bring people together, not divide them. It should exalt the human spirit, not degrade it.

Cheuk Nang Properties (Holdings) Ltd., a development firm little known outside Hong Kong, yesterday reinvented itself as a high-tech company, with plans to help bring together Mainland Chinese companies with Western partners.