Re: [PATCH v3 net-next 0/7] RDS: zerocopy support

[David Miller <davem@davemloft.net>]

From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Date: Thu, 15 Feb 2018 10:49:31 -0800

> 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.

Series applied, thanks a lot!