On Sun, Nov 18, 2018 at 8:13 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Sun, Nov 18, 2018 at 08:02:18PM +0800, Yafang Shao wrote: > > This little adjustment on bitwise operation could make the code a little > > faster. > > As write_iter is used in lots of critical path, so this code change is > > useful for performance. > > Did you check the before/after code generation with this patch applied? > Yes, I did. My oompiler is gcc-4.8.5, a litte old, and with CONFIG_CC_OPTIMIZE_FOR_SIZE on. The output file is differrent. > $ diff -u before.S after.S > --- before.S 2018-11-18 07:11:48.031096768 -0500 > +++ after.S 2018-11-18 07:11:36.883069103 -0500 > @@ -1,5 +1,5 @@ > > -before.o: file format elf32-i386 > +after.o: file format elf32-i386 > > > Disassembly of section .text: > > with gcc 8.2.0, I see no difference, indicating that the compiler already > makes this optimisation. Could pls. try set CONFIG_CC_OPTIMIZE_FOR_SIZE on and then compare them again ? Thanks Yafang
