Re: Paravirt KVM capabilities

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

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.


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