Re: [Qemu-devel] [PATCH v8 1/1] crypto: add virtio-crypto driver

[Gonglei (Arei)]

> 
> On Thu, Jan 12, 2017 at 03:10:25PM +0100, Christian Borntraeger wrote:
> > On 01/10/2017 01:56 PM, Christian Borntraeger wrote:
> > > On 01/10/2017 01:36 PM, Gonglei (Arei) wrote:
> > >> Hi,
> > >>
> > >>>
> > >>> On 12/15/2016 03:03 AM, Gonglei wrote:
> > >>> [...]
> > >>>> +
> > >>>> +static struct crypto_alg virtio_crypto_algs[] = { {
> > >>>> +      .cra_name = "cbc(aes)",
> > >>>> +      .cra_driver_name = "virtio_crypto_aes_cbc",
> > >>>> +      .cra_priority = 501,
> > >>>
> > >>>
> > >>> This is still higher than the hardware-accelerators (like intel aesni 
> > >>> or the
> > >>> s390 cpacf functions or the arm hw). aesni and s390/cpacf are supported
> by the
> > >>> hardware virtualization and available to the guests. I do not see a way
> how
> > >>> virtio
> > >>> crypto can be faster than that (in the end it might be cpacf/aesni +
> overhead)
> > >>> instead it will very likely be slower.
> > >>> So we should use a number that is higher than software implementations
> but
> > >>> lower than the hw ones.
> > >>>
> > >>> Just grepping around, the software ones seem be be around 100 and the
> > >>> hardware
> > >>> ones around 200-400. So why was 150 not enough?
> > >>>
> > >> I didn't find a documentation about how we use the priority, and I 
> > >> assumed
> > >> people use virtio-crypto will configure hardware accelerators in the
> > >> host. So I choosed the number which bigger than aesni's priority.
> > >
> > > Yes, but the aesni driver will only bind if there is HW support in the 
> > > guest.
> > > And if aesni is available in the guest (or the s390 aes function from 
> > > cpacf)
> > > it will always be faster than the same in the host via virtio.So your 
> > > priority
> > > should be smaller.
> >
> >
> > any opinion on this?
> 
> Going forward, we might add an emulated aesni device and that might
> become slower than virtio. OTOH if or when this happens, we can solve it
> by adding a priority or a feature flag to virtio to raise its priority.
> 
> So I think I agree with Christian here, let's lower the priority.
> Gonglei, could you send a patch like this?
> 
OK, will do.

Thanks,
-Gonglei