tsnep: Replace modulo operation with mask

TX/RX ring size is static and power of 2 to enable compiler to optimize
modulo operation to mask operation. Make this optimization already in
the code and don't rely on the compiler.

CPU utilisation during high packet rate has not changed. So no
performance improvement has been measured. But it is best practice to
prevent modulo operations.

Suggested-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/engleder/tsnep.h b/drivers/net/ethernet/engleder/tsnep.h
index 058c2bcf31a7f1a2eb4873bde2475b61a195ab54..1de26aec78d3d0858e5d663afb31ab7b8f61bd3d 100644 (file)
--- a/drivers/net/ethernet/engleder/tsnep.h
+++ b/drivers/net/ethernet/engleder/tsnep.h
@@ -18,6 +18,7 @@
 #define TSNEP "tsnep"
 
 #define TSNEP_RING_SIZE 256
+#define TSNEP_RING_MASK (TSNEP_RING_SIZE - 1)
 #define TSNEP_RING_RX_REFILL 16
 #define TSNEP_RING_RX_REUSE (TSNEP_RING_SIZE - TSNEP_RING_SIZE / 4)
 #define TSNEP_RING_ENTRIES_PER_PAGE (PAGE_SIZE / TSNEP_DESC_SIZE)

diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
index ed1b6102cfeb050b80ede37c3a43143db346607b..3d15e673894a234986be190561f76dbef57b43e4 100644 (file)
--- a/drivers/net/ethernet/engleder/tsnep_main.c
+++ b/drivers/net/ethernet/engleder/tsnep_main.c
@@ -292,7 +292,7 @@ static int tsnep_tx_ring_init(struct tsnep_tx *tx)
        }
        for (i = 0; i < TSNEP_RING_SIZE; i++) {
                entry = &tx->entry[i];
-               next_entry = &tx->entry[(i + 1) % TSNEP_RING_SIZE];
+               next_entry = &tx->entry[(i + 1) & TSNEP_RING_MASK];
                entry->desc->next = __cpu_to_le64(next_entry->desc_dma);
        }
 
@@ -381,7 +381,7 @@ static int tsnep_tx_map(struct sk_buff *skb, struct tsnep_tx *tx, int count)
        int i;
 
        for (i = 0; i < count; i++) {
-               entry = &tx->entry[(tx->write + i) % TSNEP_RING_SIZE];
+               entry = &tx->entry[(tx->write + i) & TSNEP_RING_MASK];
 
                if (!i) {
                        len = skb_headlen(skb);
@@ -419,7 +419,7 @@ static int tsnep_tx_unmap(struct tsnep_tx *tx, int index, int count)
        int i;
 
        for (i = 0; i < count; i++) {
-               entry = &tx->entry[(index + i) % TSNEP_RING_SIZE];
+               entry = &tx->entry[(index + i) & TSNEP_RING_MASK];
 
                if (entry->len) {
                        if (entry->type & TSNEP_TX_TYPE_SKB)
@@ -481,9 +481,9 @@ static netdev_tx_t tsnep_xmit_frame_ring(struct sk_buff *skb,
                skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
 
        for (i = 0; i < count; i++)
-               tsnep_tx_activate(tx, (tx->write + i) % TSNEP_RING_SIZE, length,
+               tsnep_tx_activate(tx, (tx->write + i) & TSNEP_RING_MASK, length,
                                  i == count - 1);
-       tx->write = (tx->write + count) % TSNEP_RING_SIZE;
+       tx->write = (tx->write + count) & TSNEP_RING_MASK;
 
        skb_tx_timestamp(skb);
 
@@ -516,7 +516,7 @@ static int tsnep_xdp_tx_map(struct xdp_frame *xdpf, struct tsnep_tx *tx,
        frag = NULL;
        len = xdpf->len;
        for (i = 0; i < count; i++) {
-               entry = &tx->entry[(tx->write + i) % TSNEP_RING_SIZE];
+               entry = &tx->entry[(tx->write + i) & TSNEP_RING_MASK];
                if (type & TSNEP_TX_TYPE_XDP_NDO) {
                        data = unlikely(frag) ? skb_frag_address(frag) :
                                                xdpf->data;
@@ -589,9 +589,9 @@ static bool tsnep_xdp_xmit_frame_ring(struct xdp_frame *xdpf,
        length = retval;
 
        for (i = 0; i < count; i++)
-               tsnep_tx_activate(tx, (tx->write + i) % TSNEP_RING_SIZE, length,
+               tsnep_tx_activate(tx, (tx->write + i) & TSNEP_RING_MASK, length,
                                  i == count - 1);
-       tx->write = (tx->write + count) % TSNEP_RING_SIZE;
+       tx->write = (tx->write + count) & TSNEP_RING_MASK;
 
        /* descriptor properties shall be valid before hardware is notified */
        dma_wmb();
@@ -691,7 +691,7 @@ static bool tsnep_tx_poll(struct tsnep_tx *tx, int napi_budget)
                /* xdpf is union with skb */
                entry->skb = NULL;
 
-               tx->read = (tx->read + count) % TSNEP_RING_SIZE;
+               tx->read = (tx->read + count) & TSNEP_RING_MASK;
 
                tx->packets++;
                tx->bytes += length + ETH_FCS_LEN;
@@ -839,7 +839,7 @@ static int tsnep_rx_ring_init(struct tsnep_rx *rx)
 
        for (i = 0; i < TSNEP_RING_SIZE; i++) {
                entry = &rx->entry[i];
-               next_entry = &rx->entry[(i + 1) % TSNEP_RING_SIZE];
+               next_entry = &rx->entry[(i + 1) & TSNEP_RING_MASK];
                entry->desc->next = __cpu_to_le64(next_entry->desc_dma);
        }
 
@@ -925,7 +925,7 @@ static int tsnep_rx_refill(struct tsnep_rx *rx, int count, bool reuse)
        int retval;
 
        for (i = 0; i < count && !alloc_failed; i++) {
-               index = (rx->write + i) % TSNEP_RING_SIZE;
+               index = (rx->write + i) & TSNEP_RING_MASK;
 
                retval = tsnep_rx_alloc_buffer(rx, index);
                if (unlikely(retval)) {
@@ -945,7 +945,7 @@ static int tsnep_rx_refill(struct tsnep_rx *rx, int count, bool reuse)
        }
 
        if (enable) {
-               rx->write = (rx->write + i) % TSNEP_RING_SIZE;
+               rx->write = (rx->write + i) & TSNEP_RING_MASK;
 
                /* descriptor properties shall be valid before hardware is
                 * notified
@@ -1090,7 +1090,7 @@ static int tsnep_rx_poll(struct tsnep_rx *rx, struct napi_struct *napi,
                                 * empty RX ring, thus buffer cannot be used for
                                 * RX processing
                                 */
-                               rx->read = (rx->read + 1) % TSNEP_RING_SIZE;
+                               rx->read = (rx->read + 1) & TSNEP_RING_MASK;
                                desc_available++;
 
                                rx->dropped++;
@@ -1117,7 +1117,7 @@ static int tsnep_rx_poll(struct tsnep_rx *rx, struct napi_struct *napi,
                 */
                length -= TSNEP_RX_INLINE_METADATA_SIZE;
 
-               rx->read = (rx->read + 1) % TSNEP_RING_SIZE;
+               rx->read = (rx->read + 1) & TSNEP_RING_MASK;
                desc_available++;
 
                if (prog) {