netdev - Re: Re: Re: [PATCH v6 10/10] Documentation: Add documentation for VDUSE

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Date:   Thu, 15 Apr 2021 15:17:47 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Re: Re: [PATCH v6 10/10] Documentation: Add documentation for
 VDUSE

On Thu, Apr 15, 2021 at 04:33:27PM +0800, Yongji Xie wrote:
> On Thu, Apr 15, 2021 at 3:19 PM Stefan Hajnoczi <stefanha@...hat.com> wrote:
> > On Thu, Apr 15, 2021 at 01:38:37PM +0800, Yongji Xie wrote:
> > > On Wed, Apr 14, 2021 at 10:15 PM Stefan Hajnoczi <stefanha@...hat.com> wrote:
> > > > On Wed, Mar 31, 2021 at 04:05:19PM +0800, Xie Yongji wrote:
> > It's not obvious to me that there is a fundamental difference between
> > the two approaches in terms of performance.
> >
> > > On the other
> > > hand, we can handle the virtqueue in a unified way for both vhost-vdpa
> > > case and virtio-vdpa case. Otherwise, userspace daemon needs to know
> > > which iova ranges need to be accessed with pread(2)/pwrite(2). And in
> > > the future, we might be able to avoid bouncing in some cases.
> >
> > Ah, I see. So bounce buffers are not used for vhost-vdpa?
> >
> 
> Yes.

Okay, in that case I understand why mmap is used and it's nice to keep
virtio-vpda and vhost-vdpa unified. Thanks!

Stefan

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