tag:blogger.com,1999:blog-8459791.post594603654533761882..comments2023-01-16T00:51:39.692-08:00Comments on A Journey in Modern Computer Architectures: Core 2 Duo: That Can Hardly Be More Optimizedabinsteinhttp://www.blogger.com/profile/09589312866039619976noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-8459791.post-2440811453950411942007-05-24T11:52:00.000-07:002007-05-24T11:52:00.000-07:00Ho Ho -Are you trying to show how little you know ...<B>Ho Ho</B> -<BR/><BR/><I>Are you trying to show how little you know about ICC and compiling in general? If yes then you succeeded.</I><BR/><BR/>I'll ask you watch your language - I will forgo your silly rudeness this time, but not next. This is a professional site and I post comments very selectively. That is no flame, no bias, and no further arguing on this policy.<BR/><BR/><BR/><I>"For your information ICC defaults to generating CPU specific code. That means there is very little you can do to get any extra speedboost from playing with compiler settings."</I><BR/><BR/>Apparently you don't know what I was speaking of in the article. Maybe I assumed too much from the readers and didn't explain the context clear enough.<BR/><BR/>All SPEC base scores are compiled with the (best) Optimized flag. The difference of a "peak" score versus a "base" score is that the peak is compiled <I>in two passes</I>, where run-time information (profile) from the first pass is used in compilation of the second.<BR/><BR/>The fact that icc does not improve C2D performance from "base" to "peak" shows C2D's default optimization (hardware speculation, prediction, etc.) is already very good for SPEC workloads, that run-time profiling information do not offer further help.<BR/><BR/><BR/><I>"Even though ICC compiles stuff at several times slower pace than GCC compiling speed doesn't mean anything at all."</I><BR/><BR/>Again you are getting completely wrong ideas. I said 2x the compile time because <I>it takes two-pass profiled compilation for a dual-socket K8 to reach the same performance level of a C2D</I>.<BR/><BR/>No matter which compiler you are using, compiling twice (once for profile generation, once for actual measurement) takes about 2x the amount of time. You actually also pay an extra run time in order to generate the profile.abinsteinhttps://www.blogger.com/profile/09589312866039619976noreply@blogger.comtag:blogger.com,1999:blog-8459791.post-5125911898848304122007-05-24T07:00:00.000-07:002007-05-24T07:00:00.000-07:00It seems the microarchitecture of Core 2 Duo is so...<I>It seems the microarchitecture of Core 2 Duo is so optimizing that there is little room for more software optimization, whereas K8 Opteron still can benefit from better compilation."</I><BR/><BR/>Are you trying to show how little you know about ICC and compiling in general? If yes then you succeeded.<BR/><BR/>For your information ICC defaults to generating CPU specific code. That means there is very little you can do to get any extra speedboost from playing with compiler settings. 9.0 targeted Pentium 4 by default, I'm not sure about newer compiler versions. That means when you didn't specify it via compiler parameters you can't even run the programs on P3 or lower, assuming that compiler did manage to use some CPU specific instructions.<BR/><BR/>With GCC I've seen up to 30% speed increase in some FP heavy code just by tuning the compiler parameters from -O0 to -Os (-O3 was slower). Of cource this is very rare and in most cases there is relatively small difference in speed.<BR/><BR/><I>"This is certainly a plus for Core 2 Duo, because nobody likes to spend 2x time to compile an optimized executable."</I><BR/><BR/>Even though ICC compiles stuff at several times slower pace than GCC compiling speed doesn't mean anything at all. I can compile every single application installed on my Gentoo box in less than 24h with my e4300@2.9GHz. glibc takes the longest with around 30 minute compile time.<BR/><BR/><BR/>Also, you made some huge mistakes in the reply you made to the post in the other thread, I'll reply to it later tonight if I get time.Ho Hohttps://www.blogger.com/profile/00177815588184912351noreply@blogger.com