On 06/19/2018 11:05 AM, Saeed Mahameed wrote:
> this is only true for XDP setup, for non XDP max stride_size can only
> be around ~3k and only for mtu > ~6k
>
> For XDP setup you suggested:
> - priv->frag_info[0].frag_size = eff_mtu;
> + priv->frag_info[0].frag_size = PAGE_SIZE;
>
> currently the condition is:
>
> release = frags->page_offset + frag_info->frag_size > PAGE_SIZE;
>
> so my solution and yours have the same problem you described above.
>
> the problem is not with the initial values or with stride/farg size
> math, it just that in XDP we shouldn't reuse at ALL. I agree with you
> that we need to optimize and maybe for PAGE_SIZE > 8k we need to allow
> XDP setup to reuses. but for now there is a data corruption to handle.
Sure, we all agree there is a bug to fix.
The way you are fixing it is kind of illogical.
The NIC can use a frag if its _size_ is big enough to receive the frame.
The _stride_ is an abstraction created by the driver to report an estimation
of the _truesize_,
or memory consumption, so that linux can better track overall memory usage.
For example, if MTU=1500, the size of the fragment is 1536 bytes, but since we
can put only
2 fragments per 4KB page (on x86), we declare the _stride_ to be 2048 bytes.
Declaring that a final blob of a page, being 1600 bytes, not able to receive a
frame because
_stride_ is 2048 is illogical and waste resources.
