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Give up on pushing CC_OPTIMIZE_FOR_SIZE

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I still happen to believe that I$ miss costs are a major thing, but
sadly, -Os doesn't seem to be the solution.  With or without it, gcc
will miss some obvious code size improvements, and with it enabled gcc
will sometimes make choices that aren't good even with high I$ miss
ratios.

For example, with -Os, gcc on x86 will turn a 20-byte constant memcpy
into a "rep movsl".  While I sincerely hope that x86 CPU's will some day
do a good job at that, they certainly don't do it yet, and the cost is
higher than a L1 I$ miss would be.

Some day I hope we can re-enable this.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2011-05-22 14:30:36 -07:00
parent 71a8638480
commit 281dc5c5ec
1 changed files with 0 additions and 1 deletions
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init/Kconfig
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@ -908,7 +908,6 @@ endif
config CC_OPTIMIZE_FOR_SIZE config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size" bool "Optimize for size"
default y
help help
Enabling this option will pass "-Os" instead of "-O2" to gcc Enabling this option will pass "-Os" instead of "-O2" to gcc
resulting in a smaller kernel. resulting in a smaller kernel.