diff options
authorMagnus Karlsson <magnus.karlsson@intel.com>2020-02-10 16:27:12 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2020-02-11 15:51:11 +0100
commit30744a68626db6a0029aca9c646831c869c16d83 (patch)
parent2bf0eb9b3b0d099b20b2c4736436b666d78b94d5 (diff)
xsk: Publish global consumer pointers when NAPI is finished
The commit 4b638f13bab4 ("xsk: Eliminate the RX batch size") introduced a much more lazy way of updating the global consumer pointers from the kernel side, by only doing so when running out of entries in the fill or Tx rings (the rings consumed by the kernel). This can result in a deadlock with the user application if the kernel requires more than one entry to proceed and the application cannot put these entries in the fill ring because the kernel has not updated the global consumer pointer since the ring is not empty. Fix this by publishing the local kernel side consumer pointer whenever we have completed Rx or Tx processing in the kernel. This way, user space will have an up-to-date view of the consumer pointers whenever it gets to execute in the one core case (application and driver on the same core), or after a certain number of packets have been processed in the two core case (application and driver on different cores). A side effect of this patch is that the one core case gets better performance, but the two core case gets worse. The reason that the one core case improves is that updating the global consumer pointer is relatively cheap since the application by definition is not running when the kernel is (they are on the same core) and it is beneficial for the application, once it gets to run, to have pointers that are as up to date as possible since it then can operate on more packets and buffers. In the two core case, the most important performance aspect is to minimize the number of accesses to the global pointers since they are shared between two cores and bounces between the caches of those cores. This patch results in more updates to global state, which means lower performance in the two core case. Fixes: 4b638f13bab4 ("xsk: Eliminate the RX batch size") Reported-by: Ryan Goodfellow <rgoodfel@isi.edu> Reported-by: Maxim Mikityanskiy <maximmi@mellanox.com> Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com> Acked-by: Maxim Mikityanskiy <maximmi@mellanox.com> Link: https://lore.kernel.org/bpf/1581348432-6747-1-git-send-email-magnus.karlsson@intel.com
2 files changed, 4 insertions, 1 deletions
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index df600487a68d..356f90e4522b 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -217,6 +217,7 @@ static int xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
static void xsk_flush(struct xdp_sock *xs)
+ __xskq_cons_release(xs->umem->fq);
@@ -304,6 +305,7 @@ void xsk_umem_consume_tx_done(struct xdp_umem *umem)
list_for_each_entry_rcu(xs, &umem->xsk_list, list) {
+ __xskq_cons_release(xs->tx);
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index bec2af11853a..89a01ac4e079 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -271,7 +271,8 @@ static inline void xskq_cons_release(struct xsk_queue *q)
/* To improve performance, only update local state here.
* Reflect this to global state when we get new entries
- * from the ring in xskq_cons_get_entries().
+ * from the ring in xskq_cons_get_entries() and whenever
+ * Rx or Tx processing are completed in the NAPI loop.