> 2016-05-27 17:22+0200, Radim Krčmář:
> > (I wonder why MacOS X doesn't read IA32_PERF_STATUS, though.)
>
> Oh, it maybe does ... we already emulate status and return 0x1000 in its
> bottom 16 bits. I have no idea what is that supposed to mean, but I
> think we should return 0x1000 in IA32_PERF_CTL then.
It's 1000, not 0x1000 (instead, on real hardware the value is typically a
multiple of 256). It was added for Darwin too.
Returning different values is okay, because they are different on real
hardware too:
(sudo dd if=/dev/cpu/0/msr skip=$((0x198)) iflag=skip_bytes bs=8 count=1;
sudo dd if=/dev/cpu/0/msr skip=$((0x199)) iflag=skip_bytes bs=8 count=1) | od -tx8
0000000 00001f3900001100 0000000000001300
^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^
PERF_STATUS PERF_CTL
And perhaps if we returned non-zero values for PERF_CTL Darwin would try to
write to it. So returning zero is fine, I think. There is no correct answer...
Paolo
> (Would be nice to understand how that 0x1000 happened ... we might want
> 0 in both.)
>
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