11.5. Anticipating Linux 2.4
Linux 2.4 changes a bit the way semaphores are implemented. Essentially, they are now more efficient because, when a semaphore is released, usually only one sleeping process is awoken.
As already mentioned, Linux 2.4 enhances support for high-end SMP architectures. It is now possible to make use of multiple external I/O APIC chips, and all the code that handles interprocessor interrupts (IPIs) has been rewritten.
However, the most important change is that Linux 2.4 is much more multithreaded than Linux 2.2. In other words, it makes use of many new spin locks and reduces the role of the global kernel lock, particularly in the networking code. Linux 2.4 is therefore much more efficient on SMP architectures and performs much better as a high-end server.
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