Re: HEADS-UP: Removal of FLIP support for xennet(4)/xvif(4)

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Mar 26, 2020 at 04:11:57PM +0100, Jaromír Dole?ek wrote:
> Hello,
> 
> I'd like to completely remove the support for old FLIP mode (page
> transfer) from xennet(4)/xvif(4)
> 
> Main consideration is that actually FLIP mode is not actually used any
> more by our oldest supported Xen 4.2, so right now it's just dead

I don't think it depends on the Xen version; only on negotiation
between frontend and backend.

Or are you saying GTF_accept_transfer isn't accepted any more ?
AFAIK code to handle it it still there in Xen 4.11, and is also used in
the mini-os example.


> code. The COPY performs better on MP systems, where the cost of page
> table manipulations and cache flushes dwarfs any gains from avoiding
> memory to memory copy.


> 
> I'm currently working on some optimisations for xennet(4), and keeping
> the FLIP code paths makes the task really convoluted, especially since
> I can't really even test it still works.

It's easy: comment out
                err = xenbus_printf(xbt, xbusd->xbusd_path,
		    "feature-rx-copy", "%d", 1);

in xennetback_xenbus_create() and the frontend should fall back to flip mode.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--