[PATCH v2 3/3] event/cnxk: use WFE in Tx fc wait

[<pbhagavatula@marvell.com>]

From: Pavan Nikhilesh <pbhagavatula@marvell.com>

Use WFE is Tx path when waiting for space in the Tx queue.
Depending upon the Tx queue contention and size, WFE will
reduce the cache pressure and power consumption.
In multi-core scenarios we have observed up to 8W power reduction.

Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
---
 drivers/event/cnxk/cn10k_tx_worker.h |  18 ++++
 drivers/net/cnxk/cn10k_tx.h          | 152 +++++++++++++++++++++++----
 2 files changed, 147 insertions(+), 23 deletions(-)

diff --git a/drivers/event/cnxk/cn10k_tx_worker.h b/drivers/event/cnxk/cn10k_tx_worker.h
index b6c9bb1d26..dea6cdcde2 100644
--- a/drivers/event/cnxk/cn10k_tx_worker.h
+++ b/drivers/event/cnxk/cn10k_tx_worker.h
@@ -24,9 +24,27 @@ cn10k_sso_hws_xtract_meta(struct rte_mbuf *m, const uint64_t *txq_data)
 static __rte_always_inline void
 cn10k_sso_txq_fc_wait(const struct cn10k_eth_txq *txq)
 {
+#ifdef RTE_ARCH_ARM64
+	uint64_t space;
+
+	asm volatile(PLT_CPU_FEATURE_PREAMBLE
+		     "		ldxr %[space], [%[addr]]		\n"
+		     "		cmp %[adj], %[space] 			\n"
+		     "		b.hi .Ldne%=				\n"
+		     "		sevl					\n"
+		     ".Lrty%=:	wfe					\n"
+		     "		ldxr %[space], [%[addr]]		\n"
+		     "		cmp %[adj], %[space]			\n"
+		     "		b.ls .Lrty%=				\n"
+		     ".Ldne%=:						\n"
+		     : [space] "=&r"(space)
+		     : [adj] "r"(txq->nb_sqb_bufs_adj), [addr] "r"(txq->fc_mem)
+		     : "memory");
+#else
 	while ((uint64_t)txq->nb_sqb_bufs_adj <=
 	       __atomic_load_n(txq->fc_mem, __ATOMIC_RELAXED))
 		;
+#endif
 }
 
 static __rte_always_inline int32_t
diff --git a/drivers/net/cnxk/cn10k_tx.h b/drivers/net/cnxk/cn10k_tx.h
index a365cbe0ee..d0e8350ce2 100644
--- a/drivers/net/cnxk/cn10k_tx.h
+++ b/drivers/net/cnxk/cn10k_tx.h
@@ -102,27 +102,72 @@ cn10k_nix_tx_mbuf_validate(struct rte_mbuf *m, const uint32_t flags)
 }
 
 static __plt_always_inline void
-cn10k_nix_vwqe_wait_fc(struct cn10k_eth_txq *txq, int64_t req)
+cn10k_nix_vwqe_wait_fc(struct cn10k_eth_txq *txq, uint16_t req)
 {
 	int64_t cached, refill;
+	int64_t pkts;
 
 retry:
+#ifdef RTE_ARCH_ARM64
+
+	asm volatile(PLT_CPU_FEATURE_PREAMBLE
+		     "		ldxr %[pkts], [%[addr]]			\n"
+		     "		tbz %[pkts], 63, .Ldne%=		\n"
+		     "		sevl					\n"
+		     ".Lrty%=:	wfe					\n"
+		     "		ldxr %[pkts], [%[addr]]			\n"
+		     "		tbnz %[pkts], 63, .Lrty%=		\n"
+		     ".Ldne%=:						\n"
+		     : [pkts] "=&r"(pkts)
+		     : [addr] "r"(&txq->fc_cache_pkts)
+		     : "memory");
+#else
+	RTE_SET_USED(pkts);
 	while (__atomic_load_n(&txq->fc_cache_pkts, __ATOMIC_RELAXED) < 0)
 		;
+#endif
 	cached = __atomic_fetch_sub(&txq->fc_cache_pkts, req, __ATOMIC_ACQUIRE) - req;
 	/* Check if there is enough space, else update and retry. */
-	if (cached < 0) {
-		/* Check if we have space else retry. */
-		do {
-			refill = txq->nb_sqb_bufs_adj -
-				 __atomic_load_n(txq->fc_mem, __ATOMIC_RELAXED);
-			refill = (refill << txq->sqes_per_sqb_log2) - refill;
-		} while (refill <= 0);
-		__atomic_compare_exchange(&txq->fc_cache_pkts, &cached, &refill,
-					  0, __ATOMIC_RELEASE,
-					  __ATOMIC_RELAXED);
+	if (cached >= 0)
+		return;
+
+	/* Check if we have space else retry. */
+#ifdef RTE_ARCH_ARM64
+	int64_t val;
+
+	asm volatile(PLT_CPU_FEATURE_PREAMBLE
+		     "		ldxr %[val], [%[addr]]			\n"
+		     "		sub %[val], %[adj], %[val]		\n"
+		     "		lsl %[refill], %[val], %[shft]		\n"
+		     "		sub %[refill], %[refill], %[val]	\n"
+		     "		sub %[refill], %[refill], %[sub]	\n"
+		     "		cmp %[refill], #0x0			\n"
+		     "		b.ge .Ldne%=				\n"
+		     "		sevl					\n"
+		     ".Lrty%=:	wfe					\n"
+		     "		ldxr %[val], [%[addr]]			\n"
+		     "		sub %[val], %[adj], %[val]		\n"
+		     "		lsl %[refill], %[val], %[shft]		\n"
+		     "		sub %[refill], %[refill], %[val]	\n"
+		     "		sub %[refill], %[refill], %[sub]	\n"
+		     "		cmp %[refill], #0x0			\n"
+		     "		b.lt .Lrty%=				\n"
+		     ".Ldne%=:						\n"
+		     : [refill] "=&r"(refill), [val] "=&r" (val)
+		     : [addr] "r"(txq->fc_mem), [adj] "r"(txq->nb_sqb_bufs_adj),
+		       [shft] "r"(txq->sqes_per_sqb_log2), [sub] "r"(req)
+		     : "memory");
+#else
+	do {
+		refill = (txq->nb_sqb_bufs_adj - __atomic_load_n(txq->fc_mem, __ATOMIC_RELAXED));
+		refill = (refill << txq->sqes_per_sqb_log2) - refill;
+		refill -= req;
+	} while (refill < 0);
+#endif
+	if (!__atomic_compare_exchange(&txq->fc_cache_pkts, &cached, &refill,
+				  0, __ATOMIC_RELEASE,
+				  __ATOMIC_RELAXED))
 		goto retry;
-	}
 }
 
 /* Function to determine no of tx subdesc required in case ext
@@ -283,10 +328,27 @@ static __rte_always_inline void
 cn10k_nix_sec_fc_wait_one(struct cn10k_eth_txq *txq)
 {
 	uint64_t nb_desc = txq->cpt_desc;
-	uint64_t *fc = txq->cpt_fc;
-
-	while (nb_desc <= __atomic_load_n(fc, __ATOMIC_RELAXED))
+	uint64_t fc;
+
+#ifdef RTE_ARCH_ARM64
+	asm volatile(PLT_CPU_FEATURE_PREAMBLE
+		     "		ldxr %[space], [%[addr]]		\n"
+		     "		cmp %[nb_desc], %[space]		\n"
+		     "		b.hi .Ldne%=				\n"
+		     "		sevl					\n"
+		     ".Lrty%=:	wfe					\n"
+		     "		ldxr %[space], [%[addr]]		\n"
+		     "		cmp %[nb_desc], %[space]		\n"
+		     "		b.ls .Lrty%=				\n"
+		     ".Ldne%=:						\n"
+		     : [space] "=&r"(fc)
+		     : [nb_desc] "r"(nb_desc), [addr] "r"(txq->cpt_fc)
+		     : "memory");
+#else
+	RTE_SET_USED(fc);
+	while (nb_desc <= __atomic_load_n(txq->cpt_fc, __ATOMIC_RELAXED))
 		;
+#endif
 }
 
 static __rte_always_inline void
@@ -294,7 +356,7 @@ cn10k_nix_sec_fc_wait(struct cn10k_eth_txq *txq, uint16_t nb_pkts)
 {
 	int32_t nb_desc, val, newval;
 	int32_t *fc_sw;
-	volatile uint64_t *fc;
+	uint64_t *fc;
 
 	/* Check if there is any CPT instruction to submit */
 	if (!nb_pkts)
@@ -302,21 +364,59 @@ cn10k_nix_sec_fc_wait(struct cn10k_eth_txq *txq, uint16_t nb_pkts)
 
 again:
 	fc_sw = txq->cpt_fc_sw;
-	val = __atomic_fetch_sub(fc_sw, nb_pkts, __ATOMIC_RELAXED) - nb_pkts;
+#ifdef RTE_ARCH_ARM64
+	asm volatile(PLT_CPU_FEATURE_PREAMBLE
+		     "		ldxr %w[pkts], [%[addr]]		\n"
+		     "		tbz %w[pkts], 31, .Ldne%=		\n"
+		     "		sevl					\n"
+		     ".Lrty%=:	wfe					\n"
+		     "		ldxr %w[pkts], [%[addr]]		\n"
+		     "		tbnz %w[pkts], 31, .Lrty%=		\n"
+		     ".Ldne%=:						\n"
+		     : [pkts] "=&r"(val)
+		     : [addr] "r"(fc_sw)
+		     : "memory");
+#else
+	/* Wait for primary core to refill FC. */
+	while (__atomic_load_n(fc_sw, __ATOMIC_RELAXED) < 0)
+		;
+#endif
+
+	val = __atomic_fetch_sub(fc_sw, nb_pkts, __ATOMIC_ACQUIRE) - nb_pkts;
 	if (likely(val >= 0))
 		return;
 
 	nb_desc = txq->cpt_desc;
 	fc = txq->cpt_fc;
+#ifdef RTE_ARCH_ARM64
+	asm volatile(PLT_CPU_FEATURE_PREAMBLE
+		     "		ldxr %[refill], [%[addr]]		\n"
+		     "		sub %[refill], %[desc], %[refill]	\n"
+		     "		sub %[refill], %[refill], %[pkts]	\n"
+		     "		cmp %[refill], #0x0			\n"
+		     "		b.ge .Ldne%=				\n"
+		     "		sevl					\n"
+		     ".Lrty%=:	wfe					\n"
+		     "		ldxr %[refill], [%[addr]]		\n"
+		     "		sub %[refill], %[desc], %[refill]	\n"
+		     "		sub %[refill], %[refill], %[pkts]	\n"
+		     "		cmp %[refill], #0x0			\n"
+		     "		b.lt .Lrty%=				\n"
+		     ".Ldne%=:						\n"
+		     : [refill] "=&r"(newval)
+		     : [addr] "r"(fc), [desc] "r"(nb_desc), [pkts] "r"(nb_pkts)
+		     : "memory");
+#else
 	while (true) {
 		newval = nb_desc - __atomic_load_n(fc, __ATOMIC_RELAXED);
 		newval -= nb_pkts;
 		if (newval >= 0)
 			break;
 	}
+#endif
 
-	if (!__atomic_compare_exchange_n(fc_sw, &val, newval, false,
-					 __ATOMIC_RELAXED, __ATOMIC_RELAXED))
+	if (!__atomic_compare_exchange_n(fc_sw, &val, newval, false, __ATOMIC_RELEASE,
+					 __ATOMIC_RELAXED))
 		goto again;
 }
 
@@ -3033,10 +3133,16 @@ cn10k_nix_xmit_pkts_vector(void *tx_queue, uint64_t *ws,
 		wd.data[1] |= ((uint64_t)(lnum - 17)) << 12;
 		wd.data[1] |= (uint64_t)(lmt_id + 16);
 
-		if (flags & NIX_TX_VWQE_F)
-			cn10k_nix_vwqe_wait_fc(txq,
-				burst - (cn10k_nix_pkts_per_vec_brst(flags) >>
-					 1));
+		if (flags & NIX_TX_VWQE_F) {
+			if (flags & NIX_TX_MULTI_SEG_F) {
+				if (burst - (cn10k_nix_pkts_per_vec_brst(flags) >> 1) > 0)
+					cn10k_nix_vwqe_wait_fc(txq,
+						burst - (cn10k_nix_pkts_per_vec_brst(flags) >> 1));
+			} else {
+				cn10k_nix_vwqe_wait_fc(txq,
+						burst - (cn10k_nix_pkts_per_vec_brst(flags) >> 1));
+			}
+		}
 		/* STEOR1 */
 		roc_lmt_submit_steorl(wd.data[1], pa);
 	} else if (lnum) {
-- 
2.25.1