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Subject: Re: [virtio-comment] Re: [EXT] Re: [virtio-comment] Re: [PATCH] virtio-net: Add equal-sized receive buffers feature

On 2019/11/25 äå4:30, Michael S. Tsirkin wrote:
On Mon, Nov 25, 2019 at 04:22:47PM +0800, Jason Wang wrote:
On 2019/11/25 äå4:18, Michael S. Tsirkin wrote:
Again I can see how we might want to disallow crazy setups with e.g. 1
byte per buffer. That's just abuse, no guest does that anyway. So asking
e.g. for a minimal buffer size sounds very reasonable.
One question here is that, the minimal buffer size should depends on various
factors. E.g the ring size. Consider a 256 entries ring, the minimal size
should be 64K/256=256 ...
I guess you are right. We can make this driver programmable I guess?
Basically pass min_buf_len to the device.
Then it still have the chance to program the min_buf_len to 1?
If it wants to - yes - presumably device won't work as well,
fetching all kind of extra data e.g. unnecessary descriptors.

Technically, device should still work for small packet and drop large
I am not sure I agree. How is this different from just not being
sufficient space in the RX ring? We certainly do not want to
drop packets just because there's not enough buffers -
it's a temporary condition.

I think not? Spec doesn't forbid e.g 1 byte buffer. So when a large packet come, if we don't drop packet. Device may think no available buffer but driver may think all buffers are available.

Vhost has a bug that will stall RX in the case.
I think we want to spec this first then.

I agree the clarification in the spec, but it wold be too late for existed drivers?


Will post a fix.


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