Re: [PATCH net-next v2 02/12] iavf: kill "legacy-rx" for good

From: Alexander Lobakin
Date: Tue May 30 2023 - 12:23:29 EST

From: Alexander H Duyck <alexander.duyck@xxxxxxxxx>
Date: Tue, 30 May 2023 08:29:10 -0700

> On Thu, 2023-05-25 at 14:57 +0200, Alexander Lobakin wrote:
>> Ever since build_skb() became stable, the old way with allocating an skb
>> for storing the headers separately, which will be then copied manually,
>> was slower, less flexible and thus obsolete.


> The "legacy-rx" was never about performance. It was mostly about
> providing a fall back in the event of an unexpected behavior. Keep in
> mind that in order to enable this we are leaving the page mapped and
> syncing it multiple times. In order to enable support for this we had
> to add several new items that I had deemed to be a bit risky such as
> support for DMA pages that were synced by the driver instead of on
> map/unmap and the use of the build_skb logic.

And now pretty much every driver doesn't do map/unmap each time and
keeps its mapping for a very long time. And now Chris noticed that and
says it's not supposed to be used like that :D

> My main concern was that if we ever ran into header corruption we
> could switch this on and then the pages would only be writable by the
> device.


> Since it has been about 6 years without any issues I would say we are
> safe to remove it.
> Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx>