linux-kernel - Re: Re: Re: Re: [PATCH v2 0/2] virtio: abstract virtqueue related methods

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Date:   Wed, 17 May 2023 06:13:17 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     zhenwei pi <pizhenwei@...edance.com>
Cc:     stefanha@...hat.com, jasowang@...hat.com,
        xuanzhuo@...ux.alibaba.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: Re: Re: [PATCH v2 0/2] virtio: abstract virtqueue related
 methods

On Wed, May 17, 2023 at 02:21:09PM +0800, zhenwei pi wrote:
> On 5/17/23 14:10, Michael S. Tsirkin wrote:
> > On Wed, May 17, 2023 at 12:58:10PM +0800, zhenwei pi wrote:
> > > On 5/17/23 11:57, Michael S. Tsirkin wrote:
> > > > On Wed, May 17, 2023 at 11:51:03AM +0800, zhenwei pi wrote:
> > > > > 
> > > > > 
> > > > > On 5/17/23 11:46, Michael S. Tsirkin wrote:
> > > > > > On Wed, May 17, 2023 at 10:54:22AM +0800, zhenwei pi wrote:
> > > > > > > v1 -> v2:
> > > > > > > - Suggested by MST, use fast path for vring based performance
> > > > > > > sensitive API.
> > > > > > > - Reduce changes in tools/virtio.
> > > > > > > 
> > > > > > > Add test result(no obvious change):
> > > > > > > Before:
> > > > > > > time ./vringh_test --parallel
> > > > > > > Using CPUS 0 and 191
> > > > > > > Guest: notified 10036893, pinged 68278
> > > > > > > Host: notified 68278, pinged 3093532
> > > > > > > 
> > > > > > > real	0m14.463s
> > > > > > > user	0m6.437s
> > > > > > > sys	0m8.010s
> > > > > > > 
> > > > > > > After:
> > > > > > > time ./vringh_test --parallel
> > > > > > > Using CPUS 0 and 191
> > > > > > > Guest: notified 10036709, pinged 68347
> > > > > > > Host: notified 68347, pinged 3085292
> > > > > > > 
> > > > > > > real	0m14.196s
> > > > > > > user	0m6.289s
> > > > > > > sys	0m7.885s
> > > > > > > 
> > > > > > > v1:
> > > > > > > Hi,
> > > > > > > 
> > > > > > > 3 weeks ago, I posted a proposal 'Virtio Over Fabrics':
> > > > > > > https://lists.oasis-open.org/archives/virtio-comment/202304/msg00442.html
> > > > > > > 
> > > > > > > Jason and Stefan pointed out that a non-vring based virtqueue has a
> > > > > > > chance to overwrite virtqueue instead of using vring virtqueue.
> > > > > > > 
> > > > > > > Then I try to abstract virtqueue related methods in this series, the
> > > > > > > details changes see the comment of patch 'virtio: abstract virtqueue related methods'.
> > > > > > > 
> > > > > > > Something is still remained:
> > > > > > > - __virtqueue_break/__virtqueue_unbreak is supposed to use by internal
> > > > > > >      virtio core, I'd like to rename them to vring_virtqueue_break
> > > > > > >      /vring_virtqueue_unbreak. Is this reasonable?
> > > > > > 
> > > > > > Why? These just set a flag?
> > > > > > 
> > > > > 
> > > > > Rename '__virtqueue_break' to 'vring_virtqueue_break', to make symbols
> > > > > exported from virtio_ring.ko have unified prefix 'vring_virtqueue_xxx'.
> > > > 
> > > > I just do not see why you need these callbacks at all.
> > > > 
> > > 
> > > I use these callbacks for break/unbreak device like:
> > > static inline void virtio_break_device(struct virtio_device *dev)
> > > {
> > > 	struct virtqueue *vq;
> > > 
> > > 	spin_lock(&dev->vqs_list_lock);
> > > 	list_for_each_entry(vq, &dev->vqs, list) {
> > > 		vq->__break(vq);
> > > 	}
> > > 	spin_unlock(&dev->vqs_list_lock);
> > > }
> > 
> > why do this? backend knows they are broken.
> > 
> 
> I grep 'virtio_break_device' in the latest code:
> arch/um/drivers/virtio_uml.c:1147:	virtio_break_device(&vu_dev->vdev);
> arch/um/drivers/virtio_uml.c:1285:	virtio_break_device(&vu_dev->vdev);
> drivers/crypto/virtio/virtio_crypto_core.c:269:	
> virtio_break_device(vcrypto->vdev);
> drivers/s390/virtio/virtio_ccw.c:1251:			virtio_break_device(&vcdev->vdev);
> drivers/s390/virtio/virtio_ccw.c:1268:		virtio_break_device(&vcdev->vdev);
> drivers/firmware/arm_scmi/virtio.c:489:
> virtio_break_device(vioch->vqueue->vdev);
> drivers/char/virtio_console.c:1956:	virtio_break_device(vdev);
> 
> Some virtio drivers use 'virtio_break_device'...

You should read the code and understand what it does,
not just grep things and make assumptions.
What virtio_break_device does is stop linux from sending
new requests.


> > > > > > > - virtqueue_get_desc_addr/virtqueue_get_avail_addr/virtqueue_get_used_addr
> > > > > > >      /virtqueue_get_vring is vring specific, I'd like to rename them like
> > > > > > >      vring_virtqueue_get_desc_addr. Is this reasonable?
> > > > > > > - there are still some functions in virtio_ring.c with prefix *virtqueue*,
> > > > > > >      for example 'virtqueue_add_split', just keep it or rename it to
> > > > > > >      'vring_virtqueue_add_split'?
> > > > > > > zhenwei pi (2):
> > > > > > >      virtio: abstract virtqueue related methods
> > > > > > >      tools/virtio: implement virtqueue in test
> > > > > > > 
> > > > > > >     drivers/virtio/virtio_ring.c | 285 +++++-----------------
> > > > > > >     include/linux/virtio.h       | 441 +++++++++++++++++++++++++++++++----
> > > > > > >     include/linux/virtio_ring.h  |  26 +++
> > > > > > >     tools/virtio/linux/virtio.h  | 355 +++++++++++++++++++++++++---
> > > > > > >     4 files changed, 807 insertions(+), 300 deletions(-)
> > > > > > > 
> > > > > > > -- 
> > > > > > > 2.20.1
> > > > > > 
> > > > > 
> > > > > -- 
> > > > > zhenwei pi
> > > > 
> > > 
> > > -- 
> > > zhenwei pi
> > 
> 
> -- 
> zhenwei pi