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From: Stefan Hajnoczi <stefanha@redhat.com>
To: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: "Kevin Wolf" <kwolf@redhat.com>,
	"Laurent Vivier" <lvivier@redhat.com>,
	qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
	qemu-devel@nongnu.org, "Jason Wang" <jasowang@redhat.com>,
	"Amit Shah" <amit@kernel.org>,
	"David Hildenbrand" <david@redhat.com>,
	"Greg Kurz" <groug@kaod.org>,
	"Raphael Norwitz" <raphael.norwitz@nutanix.com>,
	virtio-fs@redhat.com, "Eric Auger" <eric.auger@redhat.com>,
	"Hanna Reitz" <hreitz@redhat.com>,
	"Gonglei (Arei)" <arei.gonglei@huawei.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>,
	"Fam Zheng" <fam@euphon.net>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v2 0/3] virtio: increase VIRTQUEUE_MAX_SIZE to 32k
Date: Thu, 7 Oct 2021 06:23:59 +0100	[thread overview]
Message-ID: <YV6EbwMFmcIEC+za@stefanha-x1.localdomain> (raw)
In-Reply-To: <cover.1633376313.git.qemu_oss@crudebyte.com>

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On Mon, Oct 04, 2021 at 09:38:00PM +0200, Christian Schoenebeck wrote:
> At the moment the maximum transfer size with virtio is limited to 4M
> (1024 * PAGE_SIZE). This series raises this limit to its maximum
> theoretical possible transfer size of 128M (32k pages) according to the
> virtio specs:
> 
> https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-240006

Hi Christian,
I took a quick look at the code:

- The Linux 9p driver restricts descriptor chains to 128 elements
  (net/9p/trans_virtio.c:VIRTQUEUE_NUM)

- The QEMU 9pfs code passes iovecs directly to preadv(2) and will fail
  with EINVAL when called with more than IOV_MAX iovecs
  (hw/9pfs/9p.c:v9fs_read())

Unless I misunderstood the code, neither side can take advantage of the
new 32k descriptor chain limit?

Thanks,
Stefan

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WARNING: multiple messages have this Message-ID (diff)
From: Stefan Hajnoczi <stefanha@redhat.com>
To: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: "Kevin Wolf" <kwolf@redhat.com>,
	"Laurent Vivier" <lvivier@redhat.com>,
	qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
	qemu-devel@nongnu.org, "Jason Wang" <jasowang@redhat.com>,
	"Amit Shah" <amit@kernel.org>,
	"David Hildenbrand" <david@redhat.com>,
	"Raphael Norwitz" <raphael.norwitz@nutanix.com>,
	virtio-fs@redhat.com, "Eric Auger" <eric.auger@redhat.com>,
	"Hanna Reitz" <hreitz@redhat.com>,
	"Gonglei (Arei)" <arei.gonglei@huawei.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>,
	"Fam Zheng" <fam@euphon.net>
Subject: Re: [Virtio-fs] [PATCH v2 0/3] virtio: increase VIRTQUEUE_MAX_SIZE to 32k
Date: Thu, 7 Oct 2021 06:23:59 +0100	[thread overview]
Message-ID: <YV6EbwMFmcIEC+za@stefanha-x1.localdomain> (raw)
In-Reply-To: <cover.1633376313.git.qemu_oss@crudebyte.com>

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On Mon, Oct 04, 2021 at 09:38:00PM +0200, Christian Schoenebeck wrote:
> At the moment the maximum transfer size with virtio is limited to 4M
> (1024 * PAGE_SIZE). This series raises this limit to its maximum
> theoretical possible transfer size of 128M (32k pages) according to the
> virtio specs:
> 
> https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-240006

Hi Christian,
I took a quick look at the code:

- The Linux 9p driver restricts descriptor chains to 128 elements
  (net/9p/trans_virtio.c:VIRTQUEUE_NUM)

- The QEMU 9pfs code passes iovecs directly to preadv(2) and will fail
  with EINVAL when called with more than IOV_MAX iovecs
  (hw/9pfs/9p.c:v9fs_read())

Unless I misunderstood the code, neither side can take advantage of the
new 32k descriptor chain limit?

Thanks,
Stefan

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  parent reply	other threads:[~2021-10-07  8:36 UTC|newest]

Thread overview: 97+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-04 19:38 [PATCH v2 0/3] virtio: increase VIRTQUEUE_MAX_SIZE to 32k Christian Schoenebeck
2021-10-04 19:38 ` [Virtio-fs] " Christian Schoenebeck
2021-10-04 19:38 ` [PATCH v2 1/3] virtio: turn VIRTQUEUE_MAX_SIZE into a variable Christian Schoenebeck
2021-10-04 19:38   ` [Virtio-fs] " Christian Schoenebeck
2021-10-05  7:36   ` Greg Kurz
2021-10-05  7:36     ` [Virtio-fs] " Greg Kurz
2021-10-05 12:45   ` Stefan Hajnoczi
2021-10-05 12:45     ` [Virtio-fs] " Stefan Hajnoczi
2021-10-05 13:15     ` Christian Schoenebeck
2021-10-05 13:15       ` [Virtio-fs] " Christian Schoenebeck
2021-10-05 15:10       ` Stefan Hajnoczi
2021-10-05 15:10         ` [Virtio-fs] " Stefan Hajnoczi
2021-10-05 16:32         ` Christian Schoenebeck
2021-10-05 16:32           ` [Virtio-fs] " Christian Schoenebeck
2021-10-06 11:06           ` Stefan Hajnoczi
2021-10-06 11:06             ` [Virtio-fs] " Stefan Hajnoczi
2021-10-06 12:50             ` Christian Schoenebeck
2021-10-06 12:50               ` [Virtio-fs] " Christian Schoenebeck
2021-10-06 14:42               ` Stefan Hajnoczi
2021-10-06 14:42                 ` [Virtio-fs] " Stefan Hajnoczi
2021-10-07 13:09                 ` Christian Schoenebeck
2021-10-07 13:09                   ` [Virtio-fs] " Christian Schoenebeck
2021-10-07 15:18                   ` Stefan Hajnoczi
2021-10-07 15:18                     ` [Virtio-fs] " Stefan Hajnoczi
2021-10-08 14:48                     ` Christian Schoenebeck
2021-10-08 14:48                       ` [Virtio-fs] " Christian Schoenebeck
2021-10-04 19:38 ` [PATCH v2 2/3] virtio: increase VIRTQUEUE_MAX_SIZE to 32k Christian Schoenebeck
2021-10-04 19:38   ` [Virtio-fs] " Christian Schoenebeck
2021-10-05  7:16   ` Michael S. Tsirkin
2021-10-05  7:16     ` [Virtio-fs] " Michael S. Tsirkin
2021-10-05  7:35     ` Greg Kurz
2021-10-05  7:35       ` [Virtio-fs] " Greg Kurz
2021-10-05 11:17     ` Christian Schoenebeck
2021-10-05 11:17       ` [Virtio-fs] " Christian Schoenebeck
2021-10-05 11:24       ` Michael S. Tsirkin
2021-10-05 11:24         ` [Virtio-fs] " Michael S. Tsirkin
2021-10-05 12:01         ` Christian Schoenebeck
2021-10-05 12:01           ` [Virtio-fs] " Christian Schoenebeck
2021-10-04 19:38 ` [PATCH v2 3/3] virtio-9p-device: switch to 32k max. transfer size Christian Schoenebeck
2021-10-04 19:38   ` [Virtio-fs] " Christian Schoenebeck
2021-10-05  7:38 ` [PATCH v2 0/3] virtio: increase VIRTQUEUE_MAX_SIZE to 32k David Hildenbrand
2021-10-05  7:38   ` [Virtio-fs] " David Hildenbrand
2021-10-05 11:10   ` Christian Schoenebeck
2021-10-05 11:10     ` [Virtio-fs] " Christian Schoenebeck
2021-10-05 11:19     ` Michael S. Tsirkin
2021-10-05 11:19       ` [Virtio-fs] " Michael S. Tsirkin
2021-10-05 11:43       ` Christian Schoenebeck
2021-10-05 11:43         ` [Virtio-fs] " Christian Schoenebeck
2021-10-07  5:23 ` Stefan Hajnoczi [this message]
2021-10-07  5:23   ` Stefan Hajnoczi
2021-10-07 12:51   ` Christian Schoenebeck
2021-10-07 12:51     ` [Virtio-fs] " Christian Schoenebeck
2021-10-07 15:42     ` Stefan Hajnoczi
2021-10-07 15:42       ` [Virtio-fs] " Stefan Hajnoczi
2021-10-08  7:25       ` Greg Kurz
2021-10-08  7:25         ` [Virtio-fs] " Greg Kurz
2021-10-08  8:27         ` Greg Kurz
2021-10-08 14:24         ` Christian Schoenebeck
2021-10-08 14:24           ` [Virtio-fs] " Christian Schoenebeck
2021-10-08 16:08           ` Christian Schoenebeck
2021-10-08 16:08             ` [Virtio-fs] " Christian Schoenebeck
2021-10-21 15:39             ` Christian Schoenebeck
2021-10-21 15:39               ` [Virtio-fs] " Christian Schoenebeck
2021-10-25 10:30               ` Stefan Hajnoczi
2021-10-25 10:30                 ` [Virtio-fs] " Stefan Hajnoczi
2021-10-25 15:03                 ` Christian Schoenebeck
2021-10-25 15:03                   ` [Virtio-fs] " Christian Schoenebeck
2021-10-28  9:00                   ` Stefan Hajnoczi
2021-10-28  9:00                     ` [Virtio-fs] " Stefan Hajnoczi
2021-11-01 20:29                     ` Christian Schoenebeck
2021-11-01 20:29                       ` [Virtio-fs] " Christian Schoenebeck
2021-11-03 11:33                       ` Stefan Hajnoczi
2021-11-03 11:33                         ` [Virtio-fs] " Stefan Hajnoczi
2021-11-04 14:41                         ` Christian Schoenebeck
2021-11-04 14:41                           ` [Virtio-fs] " Christian Schoenebeck
2021-11-09 10:56                           ` Stefan Hajnoczi
2021-11-09 10:56                             ` [Virtio-fs] " Stefan Hajnoczi
2021-11-09 13:09                             ` Christian Schoenebeck
2021-11-09 13:09                               ` [Virtio-fs] " Christian Schoenebeck
2021-11-10 10:05                               ` Stefan Hajnoczi
2021-11-10 10:05                                 ` [Virtio-fs] " Stefan Hajnoczi
2021-11-10 13:14                                 ` Christian Schoenebeck
2021-11-10 13:14                                   ` [Virtio-fs] " Christian Schoenebeck
2021-11-10 15:14                                   ` Stefan Hajnoczi
2021-11-10 15:14                                     ` [Virtio-fs] " Stefan Hajnoczi
2021-11-10 15:53                                     ` Christian Schoenebeck
2021-11-10 15:53                                       ` [Virtio-fs] " Christian Schoenebeck
2021-11-11 16:31                                       ` Stefan Hajnoczi
2021-11-11 16:31                                         ` [Virtio-fs] " Stefan Hajnoczi
2021-11-11 17:54                                         ` Christian Schoenebeck
2021-11-11 17:54                                           ` [Virtio-fs] " Christian Schoenebeck
2021-11-15 11:54                                           ` Stefan Hajnoczi
2021-11-15 11:54                                             ` [Virtio-fs] " Stefan Hajnoczi
2021-11-15 14:32                                             ` Christian Schoenebeck
2021-11-15 14:32                                               ` [Virtio-fs] " Christian Schoenebeck
2021-11-16 11:13                                               ` Stefan Hajnoczi
2021-11-16 11:13                                                 ` [Virtio-fs] " Stefan Hajnoczi

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