Re: pvUSB backend performance

[Juergen Gross <jgross@suse.com>]

On 07/02/2015 06:41 PM, George Dunlap wrote:
> On Mon, Jun 29, 2015 at 2:36 PM, Juergen Gross <jgross@suse.com> wrote:
>> On 06/29/2015 03:22 PM, George Dunlap wrote:
>>> I think in an ideal world the toolstack will use the kernel backend if
>>> it's available, and fall back to a qemu backend if it's not available.
>>
>>
>> In case the performance is regarded to be sufficient I won't retry to
>> push a kernel backend. So there will be none in the near future.
>>
>> If the performance is not good enough I'll give the kernel backend
>> another try. If it's being accepted I probably won't do the qemu one.
>
> So if you're asking for general advice about where we think you might
> best spend your time, I don't have much of an opinion; I don't know
> who your users are nor what your priorities are as a company.
>
> If you're asking, "Would support for a qemu pv backend be accepted
> into libxl that was 30% slower than the kernel one", I would
> personally say "absolutely" (that is, if it came to a discussion, I
> would argue for it).  As David says, not relying on the kernel is
> reason enough to accept it.  The performance only needs to be good
> enough to be usable (i.e., the performance threshold for acceptance
> would be a lot lower than the numbers you've shown here).

Thanks, that was the the kind of answer I'd like to receive.

> Do note that just because SuSE has abandoned the kernel path doesn't
> preclude others from either using old "classic" kernels, or
> forward-porting (and trying to push) the PV backends themselves.  If
> the kernel support shows up in libxl before the qemu backend is ready,
> there's no reason to remove it until it's pretty clear that pvusbback
> is well and truly dead.

Sure.

Juergen