| Message ID | 20190409212517.7321-11-linux@rasmusvillemoes.dk (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | implement DYNAMIC_DEBUG_RELATIVE_POINTERS | expand |
Le 09/04/2019 à 23:25, Rasmus Villemoes a écrit : > Similar to GENERIC_BUG_RELATIVE_POINTERS, one can now relativize the > four const char* members of struct _ddebug, thus saving 16 bytes per > instance (one for each pr_debug(), dev_debug() etc. in a > CONFIG_DYNAMIC_DEBUG kernel). The asm-generic implementation seems to > work out-of-the-box, though this is only compile-tested. > > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> > --- > arch/powerpc/Kconfig | 1 + > arch/powerpc/include/asm/Kbuild | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index 2d0be82c3061..6821c8ae1d62 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -155,6 +155,7 @@ config PPC > select BUILDTIME_EXTABLE_SORT > select CLONE_BACKWARDS > select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN > + select DYNAMIC_DEBUG_RELATIVE_POINTERS if PPC64 Why only PPC64 ? Won't it work with PPC32 ? Or would it be counter-performant on 32 bits ? Christophe > select DYNAMIC_FTRACE if FUNCTION_TRACER > select EDAC_ATOMIC_SCRUB > select EDAC_SUPPORT > diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild > index a0c132bedfae..f332e202192a 100644 > --- a/arch/powerpc/include/asm/Kbuild > +++ b/arch/powerpc/include/asm/Kbuild > @@ -3,6 +3,7 @@ generated-y += syscall_table_64.h > generated-y += syscall_table_c32.h > generated-y += syscall_table_spu.h > generic-y += div64.h > +generic-y += dynamic_debug.h > generic-y += export.h > generic-y += irq_regs.h > generic-y += local64.h >
On Tue, 23 Apr 2019 17:37:33 +0200 Christophe Leroy <christophe.leroy@c-s.fr> wrote: > > --- a/arch/powerpc/Kconfig > > +++ b/arch/powerpc/Kconfig > > @@ -155,6 +155,7 @@ config PPC > > select BUILDTIME_EXTABLE_SORT > > select CLONE_BACKWARDS > > select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN > > + select DYNAMIC_DEBUG_RELATIVE_POINTERS if PPC64 > > Why only PPC64 ? Won't it work with PPC32 ? Or would it be > counter-performant on 32 bits ? Ditto arm and i386?
On 23/04/2019 21.36, Andrew Morton wrote: > On Tue, 23 Apr 2019 17:37:33 +0200 Christophe Leroy <christophe.leroy@c-s.fr> wrote: > >>> --- a/arch/powerpc/Kconfig >>> +++ b/arch/powerpc/Kconfig >>> @@ -155,6 +155,7 @@ config PPC >>> select BUILDTIME_EXTABLE_SORT >>> select CLONE_BACKWARDS >>> select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN >>> + select DYNAMIC_DEBUG_RELATIVE_POINTERS if PPC64 >> >> Why only PPC64 ? Won't it work with PPC32 ? Or would it be >> counter-performant on 32 bits ? > > Ditto arm and i386? > It's pointless on 32-bit platforms - I'm replacing absolute const char* pointers with a relative s32 offset from the _ddebug descriptor, so if sizeof(void*)==4 there's no gain. And yes, the current implementation also wouldn't work out-of-the-box for 32-bit platforms, since the asm needs to know how to properly initialize a whole struct _ddebug, which (often) contains a static_key, which in turn contains a pointer member, which both affects its size as well as its placement inside _ddebug. The C code in dynamic_debug.c would likely Just Work, but there's no point in complicating the asm part for no gain, so there are static_assert()s in place to ensure BITS_PER_LONG==64 (as well as checking the various offsetof()s etc.). [I don't think performance matters at all, it's one extra addition to access these fields, and that is only done in the rare cases where someone interacts with the dynamic_debug/control sysfs file, and when one of the activated pr_debug()s is actually hit (so a few extra instructions drown in the printk overhead).] I do now see that PPC64 does not select GENERIC_BUG_RELATIVE_POINTERS, so maybe this scheme simply doesn't work on PPC64, or nobody has done the work to reduce the sizeof(struct bug_entry) on PPC64? As I said, I've only compile-tested arm64 and ppc64. Rasmus
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 2d0be82c3061..6821c8ae1d62 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -155,6 +155,7 @@ config PPC select BUILDTIME_EXTABLE_SORT select CLONE_BACKWARDS select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN + select DYNAMIC_DEBUG_RELATIVE_POINTERS if PPC64 select DYNAMIC_FTRACE if FUNCTION_TRACER select EDAC_ATOMIC_SCRUB select EDAC_SUPPORT diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild index a0c132bedfae..f332e202192a 100644 --- a/arch/powerpc/include/asm/Kbuild +++ b/arch/powerpc/include/asm/Kbuild @@ -3,6 +3,7 @@ generated-y += syscall_table_64.h generated-y += syscall_table_c32.h generated-y += syscall_table_spu.h generic-y += div64.h +generic-y += dynamic_debug.h generic-y += export.h generic-y += irq_regs.h generic-y += local64.h
Similar to GENERIC_BUG_RELATIVE_POINTERS, one can now relativize the four const char* members of struct _ddebug, thus saving 16 bytes per instance (one for each pr_debug(), dev_debug() etc. in a CONFIG_DYNAMIC_DEBUG kernel). The asm-generic implementation seems to work out-of-the-box, though this is only compile-tested. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> --- arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/Kbuild | 1 + 2 files changed, 2 insertions(+)