On Fri, Dec 03, 2021 at 11:37:10AM +0100, Morten Brørup wrote: > > From: Morten Brørup [mailto:[email protected]] > > Sent: Thursday, 2 December 2021 14.56 > > > > > > I disagree: Negative value does not mean failure. Only -1 means > > failure. > > > > There is no -2 return value. There is no -EINVAL return value. > > > > Testing for (ret < 0) might confuse someone to think that other values > > than -1 could be returned as indication of failure, which is not the > > case when following the convention where the functions set errno and > > return -1 in case of failure. > > > > It would be different if following a convention where the functions > > return -errno in case of failure. In this case, testing (ret < 0) would > > be appropriate. > > > > So explicitly testing (ret == -1) clarifies which of the two > > conventions are relevant. > > > > I tested it on Godbolt, and (ret < 0) produces slightly smaller code than > (ret == -1) on x86-64: > > https://godbolt.org/z/3xME3jxq8 > > A binary test (Error or Data) uses 1 byte less, and a tristate test (Error, > Zero or Data) uses 3 byte less. > > Although there is no measurable performance difference for a single instance > of this kind of test, we should consider that this kind of test appears many > times in the code, so the saved bytes might add up to something slightly > significant in the instruction cache. > > My opinion is not so strong anymore... perhaps we should prefer performance > over code readability, also in this case? >
i would not expect many calls that return rte_errno to be made on the hot path. most of the use of errno / rte_errno is control but it's good to have considered it. if i start seeing a lot of error handling in hot paths i ordinarily find a way to get rid of it through various techniques.
