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05 April 2024, 19:05:47 UTC
Revision 6a8ba9d12150461acc91bd3c9124eac19e853218 authored by Eric Dumazet on 13 December 2006, 08:34:10 UTC, committed by Linus Torvalds on 13 December 2006, 17:05:48 UTC 
[PATCH] reorder struct pipe_buf_operations
 
Fields of struct pipe_buf_operations have not a precise layout (ie not
optimized to fit cache lines nor reduce cache line ping pongs)

The bufs[] array is *large* and is placed near the beginning of the
structure, so all following fields have a large offset.  This is
unfortunate because many archs have smaller instructions when using small
offsets relative to a base register.  On x86 for example, 7 bits offsets
have smaller instruction lengths.

Moving bufs[] at the end of pipe_buf_operations permits all fields to have
small offsets, and reduce text size, and icache pressure.

# size vmlinux.pre vmlinux
    text    data     bss     dec     hex filename
3268989  664356  492196 4425541  438745 vmlinux.pre
3268765  664356  492196 4425317  438665 vmlinux

So this patch reduces text size by 224 bytes on my x86_64 machine. Similar
results on ia32.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent 0a0c502
History
Tip revision: 6a8ba9d12150461acc91bd3c9124eac19e853218 authored by Eric Dumazet on 13 December 2006, 08:34:10 UTC
[PATCH] reorder struct pipe_buf_operations
Tip revision: 6a8ba9d
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