Messages in this thread | ![/](/images/icornerl.gif) | | From | Yafang Shao <> | Date | Sun, 18 Nov 2018 23:02:19 +0800 | Subject | Re: [PATCH] mm/filemap.c: minor optimization in write_iter file operation |
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On Sun, Nov 18, 2018 at 8:13 PM Matthew Wilcox <willy@infradead.org> 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
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