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authorPaul Mackerras <paulus@samba.org>2008-04-28 13:52:31 +1000
committerPaul Mackerras <paulus@samba.org>2008-04-29 15:57:34 +1000
commit745a14cc264b1832c638e41812e0cb04328b2db1 (patch)
tree427272e0a4a1f3df96f007b1df53b73d572ec63e /include
parenta01e035ebb552223c03f2d9138ffc73f2d4d3965 (diff)
downloadop-kernel-dev-745a14cc264b1832c638e41812e0cb04328b2db1.zip
op-kernel-dev-745a14cc264b1832c638e41812e0cb04328b2db1.tar.gz
[POWERPC] Add fast little-endian switch system call
This adds a system call on 64-bit platforms for switching between little-endian and big-endian modes that is much faster than doing a prctl call. This system call is handled as a special case right at the start of the system call entry code, and because it is a special case, it uses a system call number which is out of the range of normal system calls, namely 0x1ebe. Measurements with lmbench on a 4.2GHz POWER6 showed no measurable change in the speed of normal system calls with this patch. Switching endianness with this new system call takes around 60ns on a 4.2GHz POWER6, compared with around 300ns to switch endian mode with a prctl. This can provide a significant performance advantage for emulators for little-endian architectures that want to switch between big-endian and little-endian mode frequently, e.g. because they are generating instructions sequences on the fly and they want to run those sequences in little-endian mode. The other thing about this system call is that it doesn't clobber as many registers as a normal system call. It only clobbers r12. Signed-off-by: Paul Mackerras <paulus@samba.org>
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