On Thu, Dec 6, 2018 at 10:43 AM Christoph Hellwig <h...@lst.de> wrote: > > > > > (a) the dma_is_direct() function/macro uses "likely()" for the test > > I'm a little worried about that. Yes, for the common case it is > likely. But if you run a setup where you say always have an iommu > it is not, in fact it is never called in that case, but we only know > that at runtime.
Note that "likely()" doesn't have any really huge overhead - it just makes the compiler move the unlikely case out-of-line. Compared to the overhead of the indirect branch, it's simply not a huge deal, it's more a mispredict and cache layout issue. So marking something "likely()" when it isn't doesn't really penalize things too much. It's not like an exception or anything like that, it's really just a marker for better code layout. Linus _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu