linux-kernel - [RFC 0/5] virtiofs: map buffer out of virtqueue lock

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Message-ID: <20250122163154.1225353-1-eperezma@redhat.com>
Date: Wed, 22 Jan 2025 17:31:49 +0100
From: Eugenio Pérez <eperezma@...hat.com>
To: linux-kernel@...r.kernel.org,
	mst@...hat.com,
	Hanna Reitz <hreitz@...hat.com>,
	Stefano Garzarella <sgarzare@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Jason Wang <jasowang@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	German Maglione <gmaglione@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	virtualization@...ts.linux.dev
Subject: [RFC 0/5] virtiofs: map buffer out of virtqueue lock

This is useful for some setups like swiotlb or VDUSE where the DMA
operations are expensive and/or need to be performed with a write lock.

After applying this patch, fio read test goes from 1201MiB/s to
1211MiB/s.

---
Sending this series to obtain feedback if this is the right way to go.

Q: Do we need virtqueue_map_sgs? XDP directly call dma_map. Need to
profile.
TODO: Profile multiqueue.
TODO: Handling errors.
TODO: Do the same for hiprio queue.
TODO: Can we batch maps? virtiofs always sends many buffers.

Eugenio Pérez (4):
  vduse: add virtio_fs to allowed dev id
  virtiofs: Move stack sg to fuse_req
  virtio_ring: add virtqueue premapped out/in buffers support
  virtiofs: perform DMA operations out of the spinlock

Jason Wang (1):
  virtio_ring: introduce virtqueue_map/unmap_sgs()

 drivers/vdpa/vdpa_user/vduse_dev.c |   1 +
 drivers/virtio/virtio_ring.c       | 165 ++++++++++++++++++++++++++---
 fs/fuse/fuse_i.h                   |   7 ++
 fs/fuse/virtio_fs.c                |  68 +++++++-----
 include/linux/virtio.h             |  17 +++
 5 files changed, 220 insertions(+), 38 deletions(-)

-- 
2.48.1