On Fri, Sep 14, 2018 at 5:52 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > Matt attempted to add CLOCK_TAI support to the VDSO clock_gettime() > implementation, which extended the clockid switch case and added yet > another slightly different copy of the same code. > > Especially the extended switch case is problematic as the compiler tends to > generate a jump table which then requires to use retpolines. If jump tables > are disabled it adds yet another conditional to the existing maze. > > This series takes a different approach by consolidating the almost > identical functions into one implementation for high resolution clocks and > one for the coarse grained clock ids by storing the base data for each > clock id in an array which is indexed by the clock id. > > This completely eliminates the switch case and allows further > simplifications of the code base, which at the end all together gain a few > cycles performance or at least stay on par with todays code. The resulting > performance depends heavily on the micro architecture and the compiler. tglx, please consider this whole series Acked-by: Andy Lutomirski <luto@xxxxxxxxxx> Please feel free to push it top tip:x86/vdso, as long as you pull in tip/x86/urgent first. Once it lands, I'll email out a couple of follow-up patches. --Andy _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
