> >> kernel gcc binutils with mlong without mlong
> >> 4.15.7 4.9.3 2.25.1 13.4 MB/s 27.0 MB/s
> >> 4.15.7 6.4.0 2.25.1 13.4 MB/s 27.0 MB/s
> >> 4.15.7 6.4.0 2.29.1 14.4 MB/s 25.0 MB/s
> > Interesting bad results!
> >
> It's hard to understand why the performance would deteriorate so much
> but I see essentially the same behavior.
Speaking of debian kernel, it's nearly impossible to link a kernel without mlong-calls.
Compiling without mlong-calls generates this (R_PARISC_PCREL22F):
b,l external_func,%r2
nop
With -mlong-calls it is much more complex:
.LC0:
.dword P%external_func
.globl a
a:
addil LT'.LC0,%r27
ldd RT'.LC0(%r1),%r28
ldd 0(%r28),%r28
ldd 16(%r28),%r2
bve,l (%r2),%r2
Since our kernel is running in the first 4GB of RAM (even on 64bit), couldn't we instead
introduce a gcc option, e.g. "-mkernel-indirect-calls", which translates to:
ldil L%external_func, %r2 // R_PARISC_DIR21L
ldo R%external_func(%r2), %r2 // R_PARISC_DIR14R
bve,l (%r2),%r2
Does -mfast-indirect-calls has any effect at all?
I haven't seen any difference when using this option.
Thoughts?
Helge
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