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| author | Julian Wiedmann <jwi@linux.vnet.ibm.com> | 2017-12-01 12:14:50 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2017-12-03 05:35:21 +0300 |
| commit | 6d69b1f1eb7a2edf8a3547f361c61f2538e054bb (patch) | |
| tree | 11944d807ae8a95faa6a3f77491a52cbe0bd1378 /drivers/s390/net/qeth_l2_main.c | |
| parent | bc3ab70584696cb798b9e1e0ac8e6ced5fd4c3b8 (diff) | |
| download | linux-6d69b1f1eb7a2edf8a3547f361c61f2538e054bb.tar.xz | |
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_l2_main.c')
| -rw-r--r-- | drivers/s390/net/qeth_l2_main.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/s390/net/qeth_l2_main.c b/drivers/s390/net/qeth_l2_main.c index d2537c09126d..85162712d207 100644 --- a/drivers/s390/net/qeth_l2_main.c +++ b/drivers/s390/net/qeth_l2_main.c @@ -960,6 +960,7 @@ static const struct net_device_ops qeth_l2_netdev_ops = { .ndo_stop = qeth_l2_stop, .ndo_get_stats = qeth_get_stats, .ndo_start_xmit = qeth_l2_hard_start_xmit, + .ndo_features_check = qeth_features_check, .ndo_validate_addr = eth_validate_addr, .ndo_set_rx_mode = qeth_l2_set_rx_mode, .ndo_do_ioctl = qeth_do_ioctl, @@ -1010,6 +1011,7 @@ static int qeth_l2_setup_netdev(struct qeth_card *card) if (card->info.type == QETH_CARD_TYPE_OSD && !card->info.guestlan) { card->dev->hw_features = NETIF_F_SG; card->dev->vlan_features = NETIF_F_SG; + card->dev->features |= NETIF_F_SG; /* OSA 3S and earlier has no RX/TX support */ if (qeth_is_supported(card, IPA_OUTBOUND_CHECKSUM)) { card->dev->hw_features |= NETIF_F_IP_CSUM; |