Re: Paravirt KVM capabilities

Avi Kivity
2007-01-10T18:12:27Z

Ulrich Drepper wrote:
> Ingo Molnar wrote:
>
>> that alone is already ~100-200 cycles overhead, it essentially doubles
>> the null syscall overhead. It matters at millions of syscalls per second
>> workloads, 100 cycles overhead at 1 million syscalls a second means 5%
>> performance difference at 2GHz.
>>
>
> Plus, x86-64 uses only syscall which doesn't have the opportunity to be
> intercepted in ring 1, right? That's the much more important target
> going forward.
>

Agreed. 64-bit syscalls are much better with hardware assist.

[Everyone complains how x86 is loaded with 20+ years of cruft; AMD comes
and cleans it up; then we discover how 4 rings and segmentation are
actually useful]

[[Can't a paravirtualized kernel use a vdso to use int $0x80 instead of
syscall?]]

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.