| commit | 3a55fb0d9fe8e2f4594329edd58c5fd6f35a99dd | |
| author | Kirill Smelkov <kirr@mns.spb.ru> | |
| Fri, 2 Nov 2012 11:41:01 +0000 (2 15:41 +0400) | ||
| committer | Linus Torvalds <torvalds@linux-foundation.org> | |
| Wed, 16 Jan 2013 20:42:57 +0000 (16 12:42 -0800) | ||
| tree | 7198833c5bc3e7aac4b2a23282c2c4a09eae85d2 | treesnapshot (tar.gz zip) |
| parent | fbfc23ef905e41cbf621031a3d560a55a010dd54 | commitdiff |
Tell the world we gave up on pushing CC_OPTIMIZE_FOR_SIZE
In commit 281dc5c5ec0f ("Give up on pushing CC_OPTIMIZE_FOR_SIZE") we
already changed the actual default value, but the help-text still
suggested 'y'. Fix the help text too, for all the same reasons.
Sadly, -Os keeps on generating some very suboptimal code for certain
cases, to the point where any I$ miss upside is swamped by the downside.
The main ones are:
- using "rep movsb" for memcpy, even on CPU's where that is
horrendously bad for performance.
- not honoring branch prediction information, so any I$ footprint you
win from smaller code, you lose from less code density in the I$.
- using divide instructions when that is very expensive.
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
In commit 281dc5c5ec0f ("Give up on pushing CC_OPTIMIZE_FOR_SIZE") we
already changed the actual default value, but the help-text still
suggested 'y'. Fix the help text too, for all the same reasons.
Sadly, -Os keeps on generating some very suboptimal code for certain
cases, to the point where any I$ miss upside is swamped by the downside.
The main ones are:
- using "rep movsb" for memcpy, even on CPU's where that is
horrendously bad for performance.
- not honoring branch prediction information, so any I$ footprint you
win from smaller code, you lose from less code density in the I$.
- using divide instructions when that is very expensive.
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| init/Kconfig | diffblobblamehistory |