diff options
| author | Paul Mackerras <paulus@samba.org> | 2008-04-28 13:52:31 +1000 |
|---|---|---|
| committer | Paul Mackerras <paulus@samba.org> | 2008-04-29 15:57:34 +1000 |
| commit | 745a14cc264b1832c638e41812e0cb04328b2db1 (patch) | |
| tree | 427272e0a4a1f3df96f007b1df53b73d572ec63e | |
| parent | a01e035ebb552223c03f2d9138ffc73f2d4d3965 (diff) | |
[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>
| -rw-r--r-- | arch/powerpc/kernel/head_64.S | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S index 215973a2c8d5..024805e1747d 100644 --- a/arch/powerpc/kernel/head_64.S +++ b/arch/powerpc/kernel/head_64.S @@ -239,6 +239,10 @@ instruction_access_slb_pSeries: .globl system_call_pSeries system_call_pSeries: HMT_MEDIUM +BEGIN_FTR_SECTION + cmpdi r0,0x1ebe + beq- 1f +END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) mr r9,r13 mfmsr r10 mfspr r13,SPRN_SPRG3 @@ -253,6 +257,13 @@ system_call_pSeries: rfid b . /* prevent speculative execution */ +/* Fast LE/BE switch system call */ +1: mfspr r12,SPRN_SRR1 + xori r12,r12,MSR_LE + mtspr SPRN_SRR1,r12 + rfid /* return to userspace */ + b . + STD_EXCEPTION_PSERIES(0xd00, single_step) STD_EXCEPTION_PSERIES(0xe00, trap_0e) |