linux-kernel - Re: [RFC v2 4/5] virtiofs: perform DMA operations out of the spinlock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACGkMEuGSGcmMtAwGwBWfHai=yUGGcD__kjCh-z3NbK8q6oGSw@mail.gmail.com>
Date: Mon, 24 Feb 2025 10:03:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Pérez <eperezma@...hat.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Stefan Hajnoczi <stefanha@...hat.com>, 
	Hanna Reitz <hreitz@...hat.com>, linux-kernel@...r.kernel.org, 
	German Maglione <gmaglione@...hat.com>, virtualization@...ts.linux.dev, 
	Stefano Garzarella <sgarzare@...hat.com>, yama@...hat.com, Vivek Goyal <vgoyal@...hat.com>, 
	Miklos Szeredi <miklos@...redi.hu>, mst@...hat.com
Subject: Re: [RFC v2 4/5] virtiofs: perform DMA operations out of the spinlock

On Sat, Feb 22, 2025 at 1:07 AM Eugenio Pérez <eperezma@...hat.com> wrote:
>
> 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 1124MiB/s to 1191MiB/s.

What FIO parameter have you used? It might be worth trying different
sizes. It seems to be more obvious when using larger requests when I'm
testing similar optimization for virtio-blk.

And we also need to test without VDUSE, to make sure no regression in
classical setups.

Thanks

>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> ---
>  fs/fuse/virtio_fs.c | 40 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> index 1344c5782a7c..e19c78f2480e 100644
> --- a/fs/fuse/virtio_fs.c
> +++ b/fs/fuse/virtio_fs.c
> @@ -836,8 +836,19 @@ static void virtio_fs_requests_done_work(struct work_struct *work)
>
>         /* End requests */
>         list_for_each_entry_safe(req, next, &reqs, list) {
> +               unsigned int total_sgs = req->out_sgs + req->in_sgs;
> +
>                 list_del_init(&req->list);
>
> +               for (unsigned int i = 0; i < total_sgs; ++i) {
> +                       enum dma_data_direction dir = (i < req->out_sgs) ?
> +                               DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +                       dma_unmap_page(vq->vdev->dev.parent,
> +                                      sg_dma_address(&req->sg[i]),
> +                                      sg_dma_len(&req->sg[i]), dir);
> +
> +               }
> +
>                 /* blocking async request completes in a worker context */
>                 if (req->args->may_block) {
>                         struct virtio_fs_req_work *w;
> @@ -1426,6 +1437,24 @@ static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
>                 sgs[i] = &req->sg[i];
>         WARN_ON(req->out_sgs + req->in_sgs != total_sgs);
>
> +       // TODO can we change this ptr out of the lock?
> +       vq = fsvq->vq;
> +       // TODO handle this and following errors
> +       for (i = 0; i < total_sgs; i++) {
> +               struct page *page = sg_page(&req->sg[i]);
> +               enum dma_data_direction dir = (i < req->out_sgs) ?
> +                       DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +               dma_addr_t dma_addr = dma_map_page(vq->vdev->dev.parent, page,
> +                                                  req->sg[i].offset, req->sg[i].length, dir);
> +
> +               if (dma_mapping_error(vq->vdev->dev.parent, dma_addr)) {
> +                       ret = -ENOMEM;
> +                       goto out;
> +               }
> +               sg_dma_address(&req->sg[i]) = dma_addr;
> +               sg_dma_len(&req->sg[i]) = req->sg[i].length;
> +       }
> +
>         spin_lock(&fsvq->lock);
>
>         if (!fsvq->connected) {
> @@ -1434,8 +1463,8 @@ static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
>                 goto out;
>         }
>
> -       vq = fsvq->vq;
> -       ret = virtqueue_add_sgs(vq, sgs, req->out_sgs, req->in_sgs, req, GFP_ATOMIC);
> +       ret = virtqueue_add_sgs_premapped(vq, sgs, req->out_sgs,
> +                                         req->in_sgs, req, GFP_ATOMIC);
>         if (ret < 0) {
>                 spin_unlock(&fsvq->lock);
>                 goto out;
> @@ -1460,6 +1489,13 @@ static int virtio_fs_enqueue_req(struct virtio_fs_vq *fsvq,
>                 virtqueue_notify(vq);
>
>  out:
> +       for (unsigned int j = 0; ret && j < total_sgs; ++j) {
> +               enum dma_data_direction dir = (j < req->out_sgs) ?
> +                       DMA_TO_DEVICE : DMA_FROM_DEVICE;
> +               dma_unmap_page(vq->vdev->dev.parent,
> +                              sg_dma_address(&req->sg[j]),
> +                              sg_dma_len(&req->sg[j]), dir);
> +       }
>         if (ret < 0 && req->argbuf) {
>                 kfree(req->argbuf);
>                 req->argbuf = NULL;
> --
> 2.48.1
>