Mikael Pettersson wrote:
> Manfred had a version with fixed MSR values and the varying data
> in memory. Maybe that's actually faster.
The stack pointer is already changed on context switches since Ingo
changed the kernel to use per-cpu TSS segments.
Manfred's code used a tiny stack (without a valid task struct,
a different method of recovering than Linus' code). You can get that
stack down to 6 words, (3 for debug trap, 3 more for nested NMI).
Combining these leads to an IMHO beautiful hack, which does work btw:
the 6 words fit into unused parts of the per-CPU TSS (just before
tss->es). The MSR has a constant value:
wrmsr(MSR_IA32_SYSENTER_ESP, (u32) &tss->es, 0);
I found the fastest sysenter entry code looks like this:
sysenter_entry_point:
cld # Faster before sti.
sti # Re-enable interrupts after next insn.
movl -68(%esp),%esp # Load per-CPU stack from tss->esp0.
with appropriate fixups at the start of the NMI and debug trap handlers.
enjoy,
-- Jamie
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This archive was generated by hypermail 2b29 : Mon Dec 23 2002 - 22:00:30 EST