Julian Wiedmann effea096ca s390/qeth: fix GSO throughput regression ... [ Upstream commit 6d69b1f1eb ] 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: 5722963a8e ("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>		2017-12-17 15:07:57 +01:00
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block	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
char	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
cio	s390: vfio-ccw: Do not attempt to free no-op, test and tic cda.	2017-12-10 13:40:38 +01:00
crypto	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
net	s390/qeth: fix GSO throughput regression	2017-12-17 15:07:57 +01:00
scsi	License cleanup: add SPDX license identifiers to some files	2017-11-02 10:04:46 -07:00
virtio	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux	2017-05-16 09:24:44 -07:00
Makefile	virtio/s390: rename drivers/s390/kvm -> drivers/s390/virtio	2015-07-07 14:27:06 +03:00