Re: [Xen-devel] pvUSB backend performance

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Mon, Jun 29, 2015 at 2:36 PM, Juergen Gross <jgross@xxxxxxxx> 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).

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.

 -George

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