Messages in this thread | | | From | Denis Vlasenko <> | Subject | Re: [RFC] exit_thread() speedups in x86 process.c | Date | Sat, 2 Jul 2005 14:56:40 +0300 |
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On Saturday 02 July 2005 05:57, Chuck Ebbert wrote: > On Wed, 22 Jun 2005 at 04:41:47 -0400, cutaway wrote: > > > The compilers got tweaked to be able to emit > > function code to different text sections and a massive system wide code > > triage was undertaken based on "common usage scenario" profiling run data > > from the perf analysis group. > > Linux scheduler code is in its own text section already, but > that might be for profiling the code instead of for performance. > (Look for "__sched" in the source code.) > > The gains may not be as much as you think since on X86 and at least > some other archs the entire kernel is in one large page. Still, it's > got to make some kind of sense to put infrequently-used code in its > own section just to reduce cache pollution. > > I came up with this
Nice.
> but only the "__slow" part really makes sense:
80/20 rule says that 80% of code runs 20% of time, thus we need only __fast. Everything else will be by default __slow. (IOW: normal .text section is __slow, no need to add another one).
If gcc will someday get per-function support for using -O2 / -Os like optimizations, they could be added to the __fast macro.
> --- 2.6.12.1/arch/i386/kernel/vmlinux.lds.S 2004-09-03 19:55:27.000000000 -0400 > +++ 2.6.12.1-ce1/arch/i386/kernel/vmlinux.lds.S 2005-06-26 01:48:23.770212000 -0400 > @@ -16,9 +16,11 @@ SECTIONS > /* read-only */ > _text = .; /* Text and read-only data */ > .text : { > + *(.fast.text) > *(.text) > SCHED_TEXT > LOCK_TEXT > + *(.slow.text) > *(.fixup) > *(.gnu.warning) > } = 0x9090 > --- 2.6.12.1/arch/x86_64/kernel/vmlinux.lds.S 2005-06-24 00:50:21.180212000 -0400 > +++ 2.6.12.1-ce1/arch/x86_64/kernel/vmlinux.lds.S 2005-06-26 01:50:09.100212000 -0400 > @@ -15,9 +15,11 @@ SECTIONS > phys_startup_64 = startup_64 - LOAD_OFFSET; > _text = .; /* Text and read-only data */ > .text : { > + *(.fast.text) > *(.text) > SCHED_TEXT > LOCK_TEXT > + *(.slow.text) > *(.fixup) > *(.gnu.warning) > } = 0x9090 > --- 2.6.12.1/include/linux/init.h 2005-01-04 21:48:02.000000000 -0500 > +++ 2.6.12.1-ce1/include/linux/init.h 2005-06-26 01:59:29.580212000 -0400 > @@ -46,6 +46,17 @@ > #define __exitdata __attribute__ ((__section__(".exit.data"))) > #define __exit_call __attribute_used__ __attribute__ ((__section__ (".exitcall.exit"))) > > +/* > + * Probably belongs in some other header (compiler.h?) > + */ > +#ifdef CONFIG_X86 > +#define __fast __attribute__ ((__section__(".fast.text"))) > +#define __slow __attribute__ ((__section__(".slow.text"))) > +#else > +#define __fast > +#define __slow > +#endif > + > #ifdef MODULE > #define __exit __attribute__ ((__section__(".exit.text"))) > #else -- vda
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