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>
1 file changed