From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com,
virtualization@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] virtio_ring: skip cpu sync when mapping fails
Date: Tue, 12 Nov 2024 16:45:51 -0500 [thread overview]
Message-ID: <20241112164527-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CACGkMEuCx=ht2Q75xJ11EGsjuZPWcTTpGh7OyVEHCOhGDB5f7A@mail.gmail.com>
On Mon, Nov 11, 2024 at 04:36:52PM +0800, Jason Wang wrote:
> On Mon, Nov 11, 2024 at 3:30 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Nov 11, 2024 at 10:55:38AM +0800, Jason Wang wrote:
> > > There's no need to sync DMA for CPU on mapping errors. So this patch
> > > skips the CPU sync in the error handling path of DMA mapping.
> > >
> > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> >
> > DMA sync is idempotent.
> > Extra work for slow path. Why do we bother?
>
> dma_map_sg() did this, since current virtio hack sg mappings to per
> page mapping, we lose such optimization.
>
> Actually the path is not necessarily slowpath in some setups like
> swiotlb or VDUSE.
>
> Thanks
I don't get how it's not a slowpath. Example?
--
MST
next prev parent reply other threads:[~2024-11-12 21:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-11 2:55 [PATCH] virtio_ring: skip cpu sync when mapping fails Jason Wang
2024-11-11 2:59 ` Xuan Zhuo
2024-11-11 7:30 ` Michael S. Tsirkin
2024-11-11 8:36 ` Jason Wang
2024-11-12 21:45 ` Michael S. Tsirkin [this message]
2024-11-13 1:35 ` Jason Wang
2025-01-08 11:35 ` Michael S. Tsirkin
2025-01-10 3:32 ` Jason Wang
2025-01-10 8:32 ` Michael S. Tsirkin
2025-01-13 3:06 ` Jason Wang
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