svn commit: r306661 - in stable/11/sys/dev/cxgbe: . tom

[John Baldwin]

On Monday, October 10, 2016 02:09:01 PM Slawa Olhovchenkov wrote:
> On Mon, Oct 03, 2016 at 11:15:44PM +0000, John Baldwin wrote:
> 
> > Author: jhb
> > Date: Mon Oct  3 23:15:44 2016
> > New Revision: 306661
> > URL: https://svnweb.freebsd.org/changeset/base/306661
> > 
> > Log:
> >   MFC 303405: Add support for zero-copy aio_write() on TOE sockets.
> >   
> >   AIO write requests for a TOE socket on a Chelsio T4+ adapter can now
> >   DMA directly from the user-supplied buffer.  This is implemented by
> >   wiring the pages backing the user-supplied buffer and queueing special
> >   mbufs backed by raw VM pages to the socket buffer.  The TOE code
> >   recognizes these special mbufs and builds a sglist from the VM page
> >   array associated with the mbuf when queueing a work request to the TOE.
> >   
> >   Because these mbufs do not have an associated virtual address, m_data
> >   is not valid.  Thus, the AIO handler does not invoke sosend() directly
> >   for these mbufs but instead inlines portions of sosend_generic() and
> >   tcp_usr_send().
> >   
> >   An aiotx_buffer structure is used to describe the user buffer (e.g.
> >   it holds the array of VM pages and a reference to the AIO job).  The
> >   special mbufs reference this structure via m_ext.  Note that a single
> >   job might be split across multiple mbufs (e.g. if it is larger than
> >   the socket buffer size).  The 'ext_arg2' member of each mbuf gives an
> >   offset relative to the backing aiotx_buffer.  The AIO job associated
> >   with an aiotx_buffer structure is completed when the last reference to
> >   the structure is released.
> >   
> >   Zero-copy aio_write()'s for connections associated with a given
> >   adapter can be enabled/disabled at runtime via the
> >   'dev.t[45]nex.N.toe.tx_zcopy' sysctl.
> >   
> >   Sponsored by:	Chelsio Communications
> 
> Do you have any public available application patches for support this?
> May be nginx?

Applications need to use aio_read(), ideally with at least 2 buffers (so
queue two reads, then when a read completes, consume the data and do the
next read).  I'm not sure nginx will find this but so useful as web servers
tend to send a lot more data than they receive.  The only software I have
patched explicitly for this is netperf.

-- 
John Baldwin