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SubjectRe: [RFC PATCH 00/17] virtual-bus
Gregory Haskins wrote:



>> virtio is already non-kvm-specific (lguest uses it) and
>> non-pci-specific (s390 uses it).
>>
>
> Ok, then to be more specific, I need it to be more generic than it
> already is. For instance, I need it to be able to integrate with
> shm_signals.

Why?



>> If you have a good exit mitigation scheme you can cut exits by a
>> factor of 100; so the userspace exit costs are cut by the same
>> factor. If you have good copyless networking APIs you can cut the
>> cost of copies to zero (well, to the cost of get_user_pages_fast(),
>> but a kernel solution needs that too).
>>
>
> "exit mitigation' schemes are for bandwidth, not latency. For latency
> it all comes down to how fast you can signal in both directions. If
> someone is going to do a stand-alone request-reply, its generally always
> going to be at least one hypercall and one rx-interrupt. So your speed
> will be governed by your signal path, not your buffer bandwidth.
>

The userspace path is longer by 2 microseconds (for two additional
heavyweight exits) and a few syscalls. I don't think that's worthy of
putting all the code in the kernel.

--
error compiling committee.c: too many arguments to function



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