lkml.org 
[lkml]   [2012]   [Mar]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: change last level cache alignment on x86?
>> #ifdef CONFIG_X86_VSMP

>> #ifdef CONFIG_SMP
>> #define __cacheline_aligned_in_smp \
>> __attribute__((__aligned__(INTERNODE_CACHE_BYTES))) \
>> __page_aligned_data
>> #endif
>> #endif
>
> Note the #ifdef CONFIG_X86_VSMP - so the 128 bytes does not
> actually transform into __cacheline_aligned_in_smp.


Oh, sorry, I used a inappropriate example here, actually there are lot
places reference to this value, like in cscope show
INTERNODE_CACHE_BYTES usages:

1 13 arch/x86/include/asm/cache.h <<GLOBAL>>
#define INTERNODE_CACHE_BYTES (1 << INTERNODE_CACHE_SHIFT)
2 148 arch/x86/kernel/vmlinux.lds.S <<GLOBAL>>
READ_MOSTLY_DATA(INTERNODE_CACHE_BYTES)
3 190 arch/x86/kernel/vmlinux.lds.S <<GLOBAL>>
PERCPU_VADDR(INTERNODE_CACHE_BYTES, 0, :percpu)
4 285 arch/x86/kernel/vmlinux.lds.S <<GLOBAL>>
PERCPU_SECTION(INTERNODE_CACHE_BYTES)
5 48 arch/x86/mm/tlb.c <<GLOBAL>>
char pad[INTERNODE_CACHE_BYTES];
6 18 arch/x86/include/asm/cache.h <<__cacheline_aligned_in_smp>>
__attribute__((__aligned__(INTERNODE_CACHE_BYTES))) \

and also many references to INTERNODE_CACHE_SHIFT,

>
>> 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?
>
>> config X86_INTERNODE_CACHE_SHIFT
>> int
>> default "12" if X86_VSMP
>> - default "7" if NUMA
>> default X86_L1_CACHE_SHIFT
>
> Yes, removing that line would be fine I think - I think it was
> copied from the old L1 alignment of 128 bytes (which was a P4
> artifact when that CPU was the dominant platform - that's not
> been the case for a long time already).


Thanks! I will write a patch later.

>
> Could you please also do a before/after build of an x86
> defconfig with NUMA enabled and see what the alignments in the
> before/after System.map are?


So, with defconfig on x86_64, I saw much changes in System.map:
before patched after patched
...
000000000000b000 d tlb_vector_| 000000000000b000 d tlb_vector
000000000000b080 d cpu_loops_p| 000000000000b040 d cpu_loops_
...

>
> Thanks,
>
> Ingo




\
 
 \ /
  Last update: 2012-03-02 15:45    [W:0.077 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site