powerpc/pseries: Use jump labels for hcall tracepoints
authorAnton Blanchard <anton@samba.org>
Thu, 3 Jul 2014 05:52:03 +0000 (15:52 +1000)
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>
Fri, 11 Jul 2014 06:05:58 +0000 (16:05 +1000)
commitcc1adb5f32557f10f48e8febbef7278a2db9d593
treef1570219053c85fa3db71e123af26f5776c16dd5
parent8fa5d4547eb69b7ed710cb03486d33a3a5dc2ead
powerpc/pseries: Use jump labels for hcall tracepoints

hcall tracepoints add quite a few instructions to our hcall path:

plpar_hcall:
mr      r2,r2
mfcr    r0
stw     r0,8(r1)
b       164 <---- start
ld      r12,0(r2)
std     r12,32(r1)
cmpdi   r12,0
beq     164 <---- end
...

We have an unconditional branch that gets noped out during boot and
a load/compare/branch. We also store the tracepoint value to the
stack for the hcall_exit path to use.

By using jump labels we can simplify this to just a single nop that
gets replaced with a branch when the tracepoint is enabled:

plpar_hcall:
mr      r2,r2
mfcr    r0
stw     r0,8(r1)
nop <----
...

If jump labels are not enabled, we fall back to the old method.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
arch/powerpc/include/asm/jump_label.h
arch/powerpc/platforms/pseries/hvCall.S
arch/powerpc/platforms/pseries/lpar.c