diff options
| author | Julian Wiedmann <jwi@linux.vnet.ibm.com> | 2017-12-01 10:14:50 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-12-02 21:35:21 -0500 |
| commit | 6d69b1f1eb7a2edf8a3547f361c61f2538e054bb (patch) | |
| tree | 11944d807ae8a95faa6a3f77491a52cbe0bd1378 /drivers/s390/net/qeth_l3_main.c | |
| parent | bc3ab70584696cb798b9e1e0ac8e6ced5fd4c3b8 (diff) | |
s390/qeth: fix GSO throughput regression
Using GSO with small MTUs currently results in a substantial throughput
regression - which is caused by how qeth needs to map non-linear skbs
into its IO buffer elements:
compared to a linear skb, each GSO-segmented skb effectively consumes
twice as many buffer elements (ie two instead of one) due to the
additional header-only part. This causes the Output Queue to be
congested with low-utilized IO buffers.
Fix this as follows:
If the MSS is low enough so that a non-SG GSO segmentation produces
order-0 skbs (currently ~3500 byte), opt out from NETIF_F_SG. This is
where we anticipate the biggest savings, since an SG-enabled
GSO segmentation produces skbs that always consume at least two
buffer elements.
Larger MSS values continue to get a SG-enabled GSO segmentation, since
1) the relative overhead of the additional header-only buffer element
becomes less noticeable, and
2) the linearization overhead increases.
With the throughput regression fixed, re-enable NETIF_F_SG by default to
reap the significant CPU savings of GSO.
Fixes: 5722963a8e83 ("qeth: do not turn on SG per default")
Reported-by: Nils Hoppmann <niho@de.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/s390/net/qeth_l3_main.c')
| -rw-r--r-- | drivers/s390/net/qeth_l3_main.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c index e79936b50698..46a841258fc8 100644 --- a/drivers/s390/net/qeth_l3_main.c +++ b/drivers/s390/net/qeth_l3_main.c @@ -2918,6 +2918,7 @@ static const struct net_device_ops qeth_l3_osa_netdev_ops = { .ndo_stop = qeth_l3_stop, .ndo_get_stats = qeth_get_stats, .ndo_start_xmit = qeth_l3_hard_start_xmit, + .ndo_features_check = qeth_features_check, .ndo_validate_addr = eth_validate_addr, .ndo_set_rx_mode = qeth_l3_set_multicast_list, .ndo_do_ioctl = qeth_do_ioctl, @@ -2958,6 +2959,7 @@ static int qeth_l3_setup_netdev(struct qeth_card *card) card->dev->vlan_features = NETIF_F_SG | NETIF_F_RXCSUM | NETIF_F_IP_CSUM | NETIF_F_TSO; + card->dev->features |= NETIF_F_SG; } } } else if (card->info.type == QETH_CARD_TYPE_IQD) { |