On Fri, Feb 03, 2017 at 05:42:54AM +0200, Michael S. Tsirkin wrote: > On Thu, Feb 02, 2017 at 03:21:57PM -0800, John Fastabend wrote: > > Add support for XDP adjust head by allocating a 256B header region > > that XDP programs can grow into. This is only enabled when a XDP > > program is loaded. > > > > In order to ensure that we do not have to unwind queue headroom push > > queue setup below bpf_prog_add. It reads better to do a prog ref > > unwind vs another queue setup call. > > > > At the moment this code must do a full reset to ensure old buffers > > without headroom on program add or with headroom on program removal > > are not used incorrectly in the datapath. Ideally we would only > > have to disable/enable the RX queues being updated but there is no > > API to do this at the moment in virtio so use the big hammer. In > > practice it is likely not that big of a problem as this will only > > happen when XDP is enabled/disabled changing programs does not > > require the reset. There is some risk that the driver may either > > have an allocation failure or for some reason fail to correctly > > negotiate with the underlying backend in this case the driver will > > be left uninitialized. I have not seen this ever happen on my test > > systems and for what its worth this same failure case can occur > > from probe and other contexts in virtio framework. > > > > Signed-off-by: John Fastabend <john.r.fastab...@intel.com> > > So I am currently testing what I consider a cleaner way to do this: > > MERGEABLE_BUFFER_MIN_ALIGN_SHIFT by 1: > -#define MERGEABLE_BUFFER_MIN_ALIGN_SHIFT ((PAGE_SHIFT + 1) / 2) > +#define MERGEABLE_BUFFER_MIN_ALIGN_SHIFT (PAGE_SHIFT / 2 + 1) > > and then we do not need a reset as we get a free bit to store presence > of XDP buffer.
That does indeed sounds cleaner. Do you have an ETA for this? Do you mind if John's set get applied for 4.11 while you're working on a better version? adjust_head support is a blocker for virtio+xdp adoption. I think we need a compromise for 4.11.
