diff options
| author | Julian Wiedmann <jwi@linux.vnet.ibm.com> | 2017-12-01 10:14:50 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-12-16 16:25:46 +0100 |
| commit | 1d55222b14bd13724eae360976d4df430ec09495 (patch) | |
| tree | 04ecc4817bc3e8ce7b60ba1bde3e7a4f315a86bb /drivers/s390/net/qeth_l3_main.c | |
| parent | fbf0dfe7ad9f75e2b09f4f4c84219ed0d0b9b05f (diff) | |
s390/qeth: fix GSO throughput regression
[ Upstream commit 6d69b1f1eb7a2edf8a3547f361c61f2538e054bb ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 50a2dda53b8a..07555a24fade 100644 --- a/drivers/s390/net/qeth_l3_main.c +++ b/drivers/s390/net/qeth_l3_main.c @@ -3066,6 +3066,7 @@ static const struct net_device_ops qeth_l3_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_l3_do_ioctl, @@ -3122,6 +3123,7 @@ 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) { |