Messages in this thread Patch in this message | | | Date | Thu, 27 May 2004 21:55:37 -0600 | From | Andreas Dilger <> | Subject | Re: [PPC64] Remove silly debug path from get_vsid() |
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On May 28, 2004 13:16 +1000, David Gibson wrote: > This patch removes the test, replacing it with a compile time switch. > It seems to make a measurable, although small speedup to the SLB miss > path (maybe 0.5%).
Looking at include/asm-ppc64/ppcdebug.h the ifppcdebug() macro is defined:
#ifdef CONFIG_PPCDBG #define ifppcdebug(FLAGS) if (udbg_ifdebug(FLAGS)) #else #define ifppcdebug(...) if (0) #endif
so presumably if you don't select CONFIG_PPCDBG it is also a no-op unless the compiler is broken and doesn't optimize away "if (0)" stanzas. The original construct gives you the option to enable this particular debugging at runtime (without necessarily enabling all debugging at one time) if wanted.
> Index: working-2.6/include/asm-ppc64/mmu_context.h > =================================================================== > --- working-2.6.orig/include/asm-ppc64/mmu_context.h 2004-05-20 12:58:51.000000000 +1000 > +++ working-2.6/include/asm-ppc64/mmu_context.h 2004-05-27 14:22:01.088506616 +1000 > @@ -189,15 +189,15 @@ > ordinal = (((ea >> 28) & 0x1fff) * LAST_USER_CONTEXT) | (ea >> 60); > vsid = (ordinal * VSID_RANDOMIZER) & VSID_MASK; > > - ifppcdebug(PPCDBG_HTABSTRESS) { > - /* For debug, this path creates a very poor vsid distribuition. > - * A user program can access virtual addresses in the form > - * 0x0yyyyxxxx000 where yyyy = xxxx to cause multiple mappings > - * to hash to the same page table group. > - */ > - ordinal = ((ea >> 28) & 0x1fff) | (ea >> 44); > - vsid = ordinal & VSID_MASK; > - } > +#ifdef HTABSTRESS > + /* For debug, this path creates a very poor vsid distribuition. > + * A user program can access virtual addresses in the form > + * 0x0yyyyxxxx000 where yyyy = xxxx to cause multiple mappings > + * to hash to the same page table group. > + */ > + ordinal = ((ea >> 28) & 0x1fff) | (ea >> 44); > + vsid = ordinal & VSID_MASK; > +#endif /* HTABSTRESS */ > > return vsid; > } > @@ -212,11 +212,11 @@ > ordinal = (((ea >> 28) & 0x1fff) * LAST_USER_CONTEXT) | context; > vsid = (ordinal * VSID_RANDOMIZER) & VSID_MASK; > > - ifppcdebug(PPCDBG_HTABSTRESS) { > - /* See comment above. */ > - ordinal = ((ea >> 28) & 0x1fff) | (context << 16); > - vsid = ordinal & VSID_MASK; > - } > +#ifdef HTABSTRESS > + /* See comment above. */ > + ordinal = ((ea >> 28) & 0x1fff) | (context << 16); > + vsid = ordinal & VSID_MASK; > +#endif /* HTABSTRESS */ > > return vsid; > } > > -- > David Gibson | For every complex problem there is a > david AT gibson.dropbear.id.au | solution which is simple, neat and > | wrong. > http://www.ozlabs.org/people/dgibson > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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