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David S. Miller
80c6d2b8d8
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 Commitf214f915e7("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 bya91dbff551("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>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.