On Mon, Nov 27, 2017 at 07:05:22PM -0500, Mikulas Patocka wrote: > > > On Sat, 25 Nov 2017, Greg KH wrote: > > > On Mon, Nov 13, 2017 at 02:00:45PM -0500, Mikulas Patocka wrote: > > > A small patch for schedule(), so that the code goes straght in the common > > > case. > > > > > > Signed-off-by: Mikulas Patocka <mpato...@redhat.com> > > > > Was this a measurable difference? If so, great, please provide the > > numbers and how you tested in the changelog. If it can't be measured, > > then it is not worth it to add these markings > > It is much easier to make microoptimizations (such as using likely() and > unlikely()) than to measure their effect. > > If a programmer were required to measure performance every time he uses > likely() or unlikely() in his code, he wouldn't use them at all.
If you can not measure it, you should not use it. You are forgetting about the testing that was done a few years ago that found that some huge percentage (80? 75? 90?) of all of these markings were wrong and harmful or did absolutely nothing. > > as the CPU/compiler almost always knows better. > > > > thanks, > > > > greg k-h > > The compiler assumes that pointers are usually not NULL - but in this > case, they are usually NULL. The compiler can't know better (unless > profile feedback is used). If you think so, great, but prove it, otherwise you are adding markup that is not needed or could be harmful. :) thanks, greg k-h
