[dpdk-stable] [RFC PATCH v1 4/5] lib/bpf: use wait until scheme for Rx/Tx iteration

[Feifei Wang <feifei.wang2@arm.com>]

First, fix the bug that keyword const of func arg should be after "*".
This is because const before "*" means the value of "cbi" should not be
changed. But we should monitor that cbi->use changed and then we can
jump out of loop.

Second, instead of polling for cbi->use to be updated, use
wait_until_unequal api.

Fixes: a93ff62a8938 ("bpf: introduce basic Rx/Tx filters")
Cc: konstantin.ananyev@intel.com
Cc: stable@dpdk.org

Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
 lib/bpf/bpf_pkt.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/lib/bpf/bpf_pkt.c b/lib/bpf/bpf_pkt.c
index 6e8248f0d6..ed63e00219 100644
--- a/lib/bpf/bpf_pkt.c
+++ b/lib/bpf/bpf_pkt.c
@@ -111,9 +111,9 @@ bpf_eth_cbi_unuse(struct bpf_eth_cbi *cbi)
  * Waits till datapath finished using given callback.
  */
 static void
-bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
+bpf_eth_cbi_wait(struct bpf_eth_cbi *const cbi)
 {
-	uint32_t nuse, puse;
+	uint32_t puse;
 
 	/* make sure all previous loads and stores are completed */
 	rte_smp_mb();
@@ -122,11 +122,8 @@ bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
 
 	/* in use, busy wait till current RX/TX iteration is finished */
 	if ((puse & BPF_ETH_CBI_INUSE) != 0) {
-		do {
-			rte_pause();
-			rte_compiler_barrier();
-			nuse = cbi->use;
-		} while (nuse == puse);
+		rte_compiler_barrier();
+		rte_wait_until_unequal_32(&cbi->use, puse, __ATOMIC_RELAXED);
 	}
 }
 
-- 
2.25.1