linux-kernel - Re: [PATCH] virtio_ring: skip cpu sync when mapping fails

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Message-ID: <CACGkMEv_sMF5rmeaWchAbgyFd0a7-q+D_Gfejs7NpwcG-YD-YA@mail.gmail.com>
Date: Fri, 10 Jan 2025 11:32:46 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com, 
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_ring: skip cpu sync when mapping fails

On Wed, Jan 8, 2025 at 7:35 PM Michael S. Tsirkin <mst@...hat.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@...hat.com>
>
>
> So as I said, I do not get why we are optimizing error paths.
> The commit log at least needs to be improved to document
> the motivation.

As replied before. Does the following make more sense?

1) dma_map_sg() did this
2) When the driver tries to submit more buffers than SWIOTLB allows,
dma_map might fail, in these cases, bouncing is useless.

Thanks