Hi I have seen sometimes the instrumentation will actually make the speedup. My personally guess is the instrumentation may cause a better alignment of instruction. In this case the prefetch will be more effective. So it actually optimize the code cache. In this sense, you flattern at 4e-7 maybe the instrumentation cause a similar the code alignment. There are a paper before in DSN conference, that by adding small gaps at the begining of stack, it will lead to varies perfromance result. 2015年6月4日 下午5:57于 "Bill Williams" <[email protected]>写道：
> On 06/03/2015 10:43 PM, Marc Brünink wrote: > >> Dear all, >> >> I just started to look into perturbation caused by instrumentation. >> To this end I measure the execution time of a function with and without >> instrumentation and compare the resulting distributions. >> >> I attached 2 graphs: >> a.pdf: execution without any instrumentation >> b.pdf: execution with instrumentation >> >> I instrument the entry point of a function and add a call to a >> different, empty function. The function is called at a single location. >> I was wondering whether anyone can make a good guess about why there is >> a plateau at 4e-7 in b.pdf >> >> Setting any of the set* function to non-default values, e.g. switching >> off delayed parsing, did not change anything. The behaviour is very >> reproducible. >> >> There might be quite a few things going on here. But maybe someone can >> make an educated guess and point me at the right direction? >> >> The obvious first things to check are perturbations of the various > caches, particularly the instruction cache. You may as well diff the other > plausible performance counters (data cache, branch mispredictions) while > you're at it, but I'd expect a difference in icache misses that accounts > for the majority of the difference between the wall clock (B-A) and the > instructions retired (B-A), both at a macro and micro level. > > (I'd also be interested to see a similar histogram of the difference > between B and A.) > >> Marc >> >> >> _______________________________________________ >> Dyninst-api mailing list >> [email protected] >> https://lists.cs.wisc.edu/mailman/listinfo/dyninst-api >> >> > > -- > --bw > > Bill Williams > Paradyn Project > [email protected] > _______________________________________________ > Dyninst-api mailing list > [email protected] > https://lists.cs.wisc.edu/mailman/listinfo/dyninst-api >
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