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authorChristian Borntraeger <borntraeger@de.ibm.com>2015-07-23 15:24:03 +0200
committerChristian Borntraeger <borntraeger@de.ibm.com>2015-10-29 15:59:11 +0100
commit46b708ea875f14f5496109df053624199f3aae87 (patch)
tree53c5d21b613a97aaf98f087f549a3c517fa2a31c /arch/s390
parent58c383c62e1a4379cee531b56e4293211f2d5ded (diff)
downloadlinux-46b708ea875f14f5496109df053624199f3aae87.tar.bz2
KVM: s390: use simple switch statement as multiplexer
We currently do some magic shifting (by exploiting that exit codes are always a multiple of 4) and a table lookup to jump into the exit handlers. This causes some calculations and checks, just to do an potentially expensive function call. Changing that to a switch statement gives the compiler the chance to inline and dynamically decide between jump tables or inline compare and branches. In addition it makes the code more readable. bloat-o-meter gives me a small reduction in code size: add/remove: 0/7 grow/shrink: 1/1 up/down: 986/-1334 (-348) function old new delta kvm_handle_sie_intercept 72 1058 +986 handle_prog 704 696 -8 handle_noop 54 - -54 handle_partial_execution 60 - -60 intercept_funcs 120 - -120 handle_instruction 198 - -198 handle_validity 210 - -210 handle_stop 316 - -316 handle_external_interrupt 368 - -368 Right now my gcc does conditional branches instead of jump tables. The inlining seems to give us enough cycles as some micro-benchmarking shows minimal improvements, but still in noise. Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Diffstat (limited to 'arch/s390')
-rw-r--r--arch/s390/kvm/intercept.c42
1 files changed, 21 insertions, 21 deletions
diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 7365e8a46032..b4a5aa110cec 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -336,28 +336,28 @@ static int handle_partial_execution(struct kvm_vcpu *vcpu)
return -EOPNOTSUPP;
}
-static const intercept_handler_t intercept_funcs[] = {
- [0x00 >> 2] = handle_noop,
- [0x04 >> 2] = handle_instruction,
- [0x08 >> 2] = handle_prog,
- [0x10 >> 2] = handle_noop,
- [0x14 >> 2] = handle_external_interrupt,
- [0x18 >> 2] = handle_noop,
- [0x1C >> 2] = kvm_s390_handle_wait,
- [0x20 >> 2] = handle_validity,
- [0x28 >> 2] = handle_stop,
- [0x38 >> 2] = handle_partial_execution,
-};
-
int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
{
- intercept_handler_t func;
- u8 code = vcpu->arch.sie_block->icptcode;
-
- if (code & 3 || (code >> 2) >= ARRAY_SIZE(intercept_funcs))
+ switch (vcpu->arch.sie_block->icptcode) {
+ case 0x00:
+ case 0x10:
+ case 0x18:
+ return handle_noop(vcpu);
+ case 0x04:
+ return handle_instruction(vcpu);
+ case 0x08:
+ return handle_prog(vcpu);
+ case 0x14:
+ return handle_external_interrupt(vcpu);
+ case 0x1c:
+ return kvm_s390_handle_wait(vcpu);
+ case 0x20:
+ return handle_validity(vcpu);
+ case 0x28:
+ return handle_stop(vcpu);
+ case 0x38:
+ return handle_partial_execution(vcpu);
+ default:
return -EOPNOTSUPP;
- func = intercept_funcs[code >> 2];
- if (func)
- return func(vcpu);
- return -EOPNOTSUPP;
+ }
}