On 08/12/2012 09:08 PM, Patrick J. LoPresti wrote: > ... I really do think any argument for interceptors based on "speed" is > nonsense.
Amdahl's Law says that interceptor speed does matter. Amdahl's Law also applies when slowing down operations, as well as when speeding them up. One paraphrase of Amdahl's Law is, "If you speed up every floating point operation by a factor of 10, then the speed of a whole program will increase by at most 9%, because floating point operations tend to contribute at most 10% to the running time of the whole program." In the other direction, slowing down every floating point operation by a factor of 20 (and where floating point is 10% of the usual running time) will slow down the whole program by a factor of 2.9!! (10% * 20) + ((100% - 10%) * 1) = 290%. *This* is the really eye-opening application of Amdahl's Law! In the case at hand, we are interested in string operations, not floating point. Suppose that stpncpy contributes 0.25% (1/400) of the normal running time. Then instruction-by-instruction emulation of stpncpy by memcheck is about 20 * 0.25% = 5% of the normal running time. This exceeds the common human perception threshold of 3%. In contrast, an intercepted (re-directed) stpncpy would be imperceptible. -- ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
