Semaphore Complexity

The RCU changes to the System V IPC implementations inflicted less than 5% expansion of code size, as shown in Table 6. This change increased the overall code size by only 151 lines. The RCU implememtation itself (which is also used by both module unloading and the IP route cache) adds only an additional 408 lines of code. This order-of-magnitude performance benefit is well worth the modest increase in complexity.

Table 6: Semaphore Change in Lines of Code

				Total Lines
	Ins/Del/Delta			New	Old	% Delta
msg.c	23	26	-3	885	888	-0.34%
sem.c	29	30	-1	1289	1290	-0.08%
shm.c	102	69	33	785	752	4.39%
util.c	178	13	165	581	416	39.66%
util.h	10	53	-43	64	107	-40.19%
Total	342	191	151	3604	3453	4.37%

Of course, the system-level performance increase is a much smaller 5.3%. On the other hand, the 151-line increase in code size is an insignificant fraction of the 11.7 million lines of code in the full kernel, and even this does not include the size of the database and other software involved in the benchmark.