Merge branch 'RDS-zerocopy-support'
Sowmini Varadhan says:
====================
RDS: zerocopy support
This is version 3 of the series, following up on review comments for
http://patchwork.ozlabs.org/project/netdev/list/?series=28530
Review comments addressed
Patch 4
- fix fragile use of skb->cb[], do not set ee_code incorrectly.
Patch 5:
- remove needless bzero of skb->cb[], consolidate err cleanup
A brief overview of this feature follows.
This patch series provides support for MSG_ZERCOCOPY
on a PF_RDS socket based on the APIs and infrastructure added
by Commit f214f915e7db ("tcp: enable MSG_ZEROCOPY")
For single threaded rds-stress testing using rds-tcp with the
ixgbe driver using 1M message sizes (-a 1M -q 1M) preliminary
results show that there is a significant reduction in latency: about
90 usec with zerocopy, compared with 200 usec without zerocopy.
This patchset modifies the above for zerocopy in the following manner.
- if the MSG_ZEROCOPY flag is specified with rds_sendmsg(), and,
- if the SO_ZEROCOPY socket option has been set on the PF_RDS socket,
application pages sent down with rds_sendmsg are pinned. The pinning
uses the accounting infrastructure added by a91dbff551a6 ("sock: ulimit
on MSG_ZEROCOPY pages"). The message is unpinned when all references
to the message go down to 0, and the message is freed by rds_message_purge.
A multithreaded application using this infrastructure must send down
a unique 32 bit cookie as ancillary data with each sendmsg invocation.
The format of this ancillary data is described in Patch 5 of the series.
The cookie is passed up to the application on the sk_error_queue when
the message is unpinned, indicating to the application that it is now
safe to free/reuse the message buffer. The details of the completion
notification are provided in Patch 4 of this series.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
