On Fri, Dec 08, 2017 at 03:30:18PM +0100, Pavel Machek wrote: > On Thu 2017-11-30 08:07:44, Greg KH wrote: > > On Thu, Nov 30, 2017 at 02:04:01AM -0500, Mikulas Patocka wrote: > > > > > > > > > On Tue, 28 Nov 2017, Greg KH wrote: > > > > > > > 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 <[email protected]> > > > > > > > > > > > > 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. > > > > > > The whole kernel has 19878 likely/unlikely tags. > > > > And most of them are wrong. Don't add new ones unless you can prove it > > is correct. > > _Most_ of them wrong? Really? Where is your data for _that_?
Andi Kleen ran tests about 5 years ago or so which showed this. It's in the archives somewhere... greg k-h
