> From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On Behalf Of Maciej > Fijalkowski > Sent: Thursday, September 1, 2022 4:11 PM > To: intel-wired-lan@xxxxxxxxxxxxxxxx > Cc: alasdair.mcwilliam@xxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; > bpf@xxxxxxxxxxxxxxx; Karlsson, Magnus <magnus.karlsson@xxxxxxxxx> > Subject: [Intel-wired-lan] [PATCH v3 intel-net 1/2] ice: xsk: change batched Tx > descriptor cleaning > > AF_XDP Tx descriptor cleaning in ice driver currently works in a "lazy" > way - descriptors are not cleaned immediately after send. We rather hold on with > cleaning until we see that free space in ring drops below particular threshold. This > was supposed to reduce the amount of unnecessary work related to cleaning and > instead of keeping the ring empty, ring was rather saturated. > > In AF_XDP realm cleaning Tx descriptors implies producing them to CQ. > This is a way of letting know user space that particular descriptor has been sent, > as John points out in [0]. > > We tried to implement serial descriptor cleaning which would be used in > conjunction with batched cleaning but it made code base more convoluted and > probably harder to maintain in future. Therefore we step away from batched > cleaning in a current form in favor of an approach where we set RS bit on every > last descriptor from a batch and clean always at the beginning of ice_xmit_zc(). > > This means that we give up a bit of Tx performance, but this doesn't hurt l2fwd > scenario which is way more meaningful than txonly as this can be treaten as > AF_XDP based packet generator. l2fwd is not hurt due to the fact that Tx side is > much faster than Rx and Rx is the one that has to catch Tx up. > > FWIW Tx descriptors are still produced in a batched way. > > [0]: https://lore.kernel.org/bpf/62b0a20232920_3573208ab@john.notmuch/ > > Fixes: 126cdfe1007a ("ice: xsk: Improve AF_XDP ZC Tx and use batching API") > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> > --- > drivers/net/ethernet/intel/ice/ice_txrx.c | 2 +- > drivers/net/ethernet/intel/ice/ice_xsk.c | 143 +++++++++------------- > drivers/net/ethernet/intel/ice/ice_xsk.h | 7 +- > 3 files changed, 64 insertions(+), 88 deletions(-) > Tested-by: George Kuruvinakunnel <george.kuruvinakunnel@xxxxxxxxx>
