* Randy Dunlap ([EMAIL PROTECTED]) wrote: > On Tue, 18 Sep 2007 17:07:49 -0400 Mathieu Desnoyers wrote: > > > Immediate values provide a way to use dynamic code patching to update > > variables > > sitting within the instruction stream. It saves caches lines normally used > > by > > static read mostly variables. Enable it by default, but let users disable it > > through the EMBEDDED menu with the "Disable immediate values" submenu entry. > > > > Note: Since I think that I really should let embedded systems developers > > using > > RO memory the option to disable the immediate values, I choose to leave this > > menu option there, in the EMBEDDED menu. Also, the "CONFIG_IMMEDIATE" makes > > sense because we want to compile out all the immediate code when we decide > > not > > to use optimized immediate values at all (it removes otherwise unused code). > > > > Signed-off-by: Mathieu Desnoyers <[EMAIL PROTECTED]> > > CC: Adrian Bunk <[EMAIL PROTECTED]> > > CC: Andi Kleen <[EMAIL PROTECTED]> > > CC: Alexey Dobriyan <[EMAIL PROTECTED]> > > CC: Christoph Hellwig <[EMAIL PROTECTED]> > > --- > > init/Kconfig | 21 +++++++++++++++++++++ > > 1 file changed, 21 insertions(+) > > > > Index: linux-2.6-lttng/init/Kconfig > > =================================================================== > > --- linux-2.6-lttng.orig/init/Kconfig 2007-09-18 10:09:40.000000000 > > -0400 > > +++ linux-2.6-lttng/init/Kconfig 2007-09-18 13:14:58.000000000 -0400 > > @@ -407,6 +407,17 @@ config CC_OPTIMIZE_FOR_SIZE > > config SYSCTL > > bool > > > > +config IMMEDIATE > > + default y if !DISABLE_IMMEDIATE > > So DISABLE_IMMEDIATE is just an intermediate symbol to make this option > be displayed in the EMBEDDED menu instead of in the General Setup menu ? >
I simply prefer to use a positive logic (CONFIG_IMMEDIATE) rather than the opposite. It makes makefiles and ifdefs much cleaner. Actually, the IMMEDIATE config option is not shown in any menu at all; it is totally controlled by DISABLE_IMMEDIATE. And yes, DISABLE_IMMEDIATE appears in the embedded menu. > > > + depends on X86_32 || PPC || PPC64 > > + bool > > + help > > + Immediate values are used as read-mostly variables that are rarely > > + updated. They use code patching to modify the values inscribed in the > > + instruction stream. It provides a way to save precious cache lines > > + that would otherwise have to be used by these variables. They can be > > + disabled through the EMBEDDED menu. > > + > > menuconfig EMBEDDED > > bool "Configure standard kernel features (for small systems)" > > help > > @@ -646,6 +657,16 @@ config PROC_KPAGEMAP > > information on page-level memory usage. Disabling this interface > > will reduce the size of the kernel by around 600 bytes. > > > > +config DISABLE_IMMEDIATE > > + default y if EMBEDDED > > + bool "Disable immediate values" if EMBEDDED > > + depends on X86_32 || PPC || PPC64 > > + help > > + Disable code patching based immediate values for embedded systems. It > > + consumes slightly more memory and requires to modify the instruction > > + stream each time a variable is updated. Should really be disabled for > > + embedded systems with read-only text. > > + > > endmenu # General setup > > > > config RT_MUTEXES > > --- > ~Randy > *** Remember to use Documentation/SubmitChecklist when testing your code *** -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
