Re: [Qemu-devel] [virtio-dev] RE: [PATCH v7 09/12] virtio-crypto: add data queue processing handler

[Stefan Hajnoczi]

On Mon, Oct 17, 2016 at 06:29:42AM +0000, Gonglei (Arei) wrote:
> 
> > -----Original Message-----
> > From: Stefan Hajnoczi [mailto:address@hidden
> > Sent: Sunday, October 16, 2016 9:23 PM
> > Subject: Re: [Qemu-devel] [PATCH v7 09/12] virtio-crypto: add data queue
> > processing handler
> > 
> > On Thu, Oct 13, 2016 at 03:12:03PM +0800, Gonglei wrote:
> > > Introduces VirtIOCryptoReq structure to store
> > > crypto request so that we can support sync and async
> > > crypto operation in the future.
> > 
> > What do you mean by "sync and async" operations?
> > 
> Synchronous and asynchronous.

I understand the words but:

1. The virtio interface is always asynchronous because request
   submission and completion on the virtqueue are separate steps (kick
   and irq).  The guest always thinks the operation is asynchronous.

2. If you implement operations synchronously inside QEMU then monitor
   and other QEMU threads could be blocked.  Also you will not be able
   to take advantage of parallel requests to the hardware crypto
   accelerator!

So I think it makes sense to implement everything asynchronously.

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