字节对齐问题

walleeee

回复 9# bruceteen


    16字节对齐居多。

safedead

[quote][size=2][color=#000]walleeee 发表于 2012-05-15 20:12[/color] [url=forum.php?mod=redirect&goto=findpost&pid=22101886&ptid=3743667][img]static/image/common/back.gif[/img][/url][/size]
回复 9# bruceteen


[/quote]

昨天看Intel的一篇程序开发优化手册，多次提到16字节对齐，这是其中一段
...
Assembly/Compiler Coding Rule 45. (H impact, H generality) Align data on
natural operand size address boundaries. If the data will be accessed with vector
instruction loads and stores, align the data on 16-byte boundaries.
...

文中还多次强调要时刻记住cache line的大小是64字节(当前主流Intel x86/x64)，尽量不要跨64字节边界访问以提高CACHE的效率
....
Misaligned data access can incur significant performance penalties. This is particu-
larly true for cache line splits. The size of a cache line is 64 bytes in the Pentium 4 and
other recent Intel processors, including processors based on Intel Core microarchi-
tecture.

....

On Intel Core 2 Duo, Intel Core Duo, Intel Core Solo, Pentium 4, Intel Xeon and
Pentium M processors, memory coherence is maintained on 64-byte cache lines
(rather than 32-byte cache lines. as in earlier processors). This can increase the
opportunity for false sharing.


这里我有个疑问，那就是针对64字节cache line大小而产生的优化手段一般是编译器干的事情吧
C程序员需要考虑吗？

folklore

回复 10# bruceteen
**. Happy every day~~


   

walleeee

回复 12# safedead


    不要考虑