[PATCH 4.4 16/30] hv_netvsc: use skb_get_hash() instead of a homegrown implementation

Greg Kroah-Hartman
2017-03-24T18:13:04Z

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit 757647e10e55c01fb7a9c4356529442e316a7c72 upstream.

Recent changes to 'struct flow_keys' (e.g commit d34af823ff40 ("net: Add
VLAN ID to flow_keys")) introduced a performance regression in netvsc
driver. Is problem is, however, not the above mentioned commit but the
fact that netvsc_set_hash() function did some assumptions on the struct
flow_keys data layout and this is wrong.

Get rid of netvsc_set_hash() by switching to skb_get_hash(). This change
will also imply switching to Jenkins hash from the currently used Toeplitz
but it seems there is no good excuse for Toeplitz to stay.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/net/hyperv/netvsc_drv.c | 67 +---------------------------------------
1 file changed, 3 insertions(+), 64 deletions(-)

--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -197,65 +197,6 @@ static void *init_ppi_data(struct rndis_
return ppi;
}

-union sub_key {
- u64 k;
- struct {
- u8 pad[3];
- u8 kb;
- u32 ka;
- };
-};
-
-/* Toeplitz hash function
- * data: network byte order
- * return: host byte order
- */
-static u32 comp_hash(u8 *key, int klen, void *data, int dlen)
-{
- union sub_key subk;
- int k_next = 4;
- u8 dt;
- int i, j;
- u32 ret = 0;
-
- subk.k = 0;
- subk.ka = ntohl(*(u32 *)key);
-
- for (i = 0; i < dlen; i++) {
- subk.kb = key[k_next];
- k_next = (k_next + 1) % klen;
- dt = ((u8 *)data)[i];
- for (j = 0; j < 8; j++) {
- if (dt & 0x80)
- ret ^= subk.ka;
- dt <<= 1;
- subk.k <<= 1;
- }
- }
-
- return ret;
-}
-
-static bool netvsc_set_hash(u32 *hash, struct sk_buff *skb)
-{
- struct flow_keys flow;
- int data_len;
-
- if (!skb_flow_dissect_flow_keys(skb, &flow, 0) ||
- !(flow.basic.n_proto == htons(ETH_P_IP) ||
- flow.basic.n_proto == htons(ETH_P_IPV6)))
- return false;
-
- if (flow.basic.ip_proto == IPPROTO_TCP)
- data_len = 12;
- else
- data_len = 8;
-
- *hash = comp_hash(netvsc_hash_key, HASH_KEYLEN, &flow, data_len);
-
- return true;
-}
-
static u16 netvsc_select_queue(struct net_device *ndev, struct sk_buff *skb,
void *accel_priv, select_queue_fallback_t fallback)
{
@@ -268,11 +209,9 @@ static u16 netvsc_select_queue(struct ne
if (nvsc_dev == NULL || ndev->real_num_tx_queues <= 1)
return 0;

- if (netvsc_set_hash(&hash, skb)) {
- q_idx = nvsc_dev->send_table[hash % VRSS_SEND_TAB_SIZE] %
- ndev->real_num_tx_queues;
- skb_set_hash(skb, hash, PKT_HASH_TYPE_L3);
- }
+ hash = skb_get_hash(skb);
+ q_idx = nvsc_dev->send_table[hash % VRSS_SEND_TAB_SIZE] %
+ ndev->real_num_tx_queues;

return q_idx;
}