Messages in this thread | | | Date | Mon, 27 Nov 2017 19:05:22 -0500 (EST) | From | Mikulas Patocka <> | Subject | Re: [PATCH] schedule: use unlikely() |
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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 <mpatocka@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.
> 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).
Mikulas
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