Messages in this thread Patch in this message | | | Subject | Re: change last level cache alignment on x86? | From | Alex Shi <> | Date | Fri, 02 Mar 2012 15:30:25 +0800 |
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On Thu, 2012-03-01 at 16:33 +0800, Alex,Shi wrote: > Currently last level defined in kernel is still 128 bytes, but actually > I checked intel's core2, NHM, SNB, atom, serial platforms, all of them > are using 64 bytes. > I did not get detailed info on AMD platforms. Guess someone like to give > the info here. So, Is if it possible to do the similar following changes > to use 64 byte cache alignment in kernel? > > === > diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu > index 3c57033..f342a5a 100644 > --- a/arch/x86/Kconfig.cpu > +++ b/arch/x86/Kconfig.cpu > @@ -303,7 +303,7 @@ config X86_GENERIC > config X86_INTERNODE_CACHE_SHIFT > int > default "12" if X86_VSMP > - default "7" if NUMA > + default "7" if NUMA && (MPENTIUM4) > default X86_L1_CACHE_SHIFT > > config X86_CMPXCHG
In arch/x86/include/asm/cache.h, the INTERNODE_CACHE_SHIFT macro will transfer to '__cacheline_aligned_in_smp' finally.
#ifdef CONFIG_X86_VSMP #ifdef CONFIG_SMP #define __cacheline_aligned_in_smp \ __attribute__((__aligned__(INTERNODE_CACHE_BYTES))) \ __page_aligned_data #endif #endif
look at the following contents in Kconfig.cpu, I wondering if it is possible to remove 'default "7" if NUMA' line. Then a thin and fit cache alignment will be potential helpful on performance. Anyone like to give some comments?
=== diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index 3c57033..6443c6f 100644 --- a/arch/x86/Kconfig.cpu +++ b/arch/x86/Kconfig.cpu @@ -303,7 +303,6 @@ config X86_GENERIC config X86_INTERNODE_CACHE_SHIFT int default "12" if X86_VSMP - default "7" if NUMA default X86_L1_CACHE_SHIFT config X86_CMPXCHG ==== some contents in Kconfig.cpu:
config X86_INTERNODE_CACHE_SHIFT int default "12" if X86_VSMP default "7" if NUMA && (MPENTIUM4 || MPSC) default X86_L1_CACHE_SHIFT config X86_CMPXCHG def_bool X86_64 || (X86_32 && !M386) config X86_L1_CACHE_SHIFT int default "7" if MPENTIUM4 || MPSC default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU default "4" if MELAN || M486 || M386 || MGEODEGX1 default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
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