David P. Reed wrote:
Replace use of outb to "unused" diagnostic port 0x80 for time delay
with udelay based time delay on x86_64 architecture machines. Fix for
bugs 9511 and 6307 in bugzilla, plus bugs reported in
bugzilla.redhat.com.
Derived from suggestion (that didn't compile) by Pavel Machek, and
tested, also based on measurements of typical timings of out's
collated by Rene Herman from many in the community.
This patch fixes a number of bugs known to cause problems on HP
Pavilion dv9000z and dv6000z laptops - in the form of solid freezes
when hwclock is used to show or set the time. Also, it potentially
improves bus utilization on SMP machines, by using a waiting process
that doesn't tie up the ISA/LPC bus for 1 or 2 microseconds.
kvm will forward a virtual machine's writes to port 0x80 to the real
port. The reason is that the write is much faster than exiting and
emulating it; the difference is measurable when compiling kernels.
Now if the cause is simply writing to port 0x80, then we must stop doing
that. But if the reason is the back-to-back writes, when we can keep
it, since the other writes will be trapped by kvm and emulated. Do you
which is the case?
--
Any sufficiently difficult bug is indistinguishable from a feature.
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