On Thu, 16 Jun 2011 14:42:54 +0200 Bernard Metzler wrote:
> ---
> Documentation/networking/siw.txt | 156
> ++++++++++++++++++++++++++++++++++++++
> 1 files changed, 156 insertions(+), 0 deletions(-)
> create mode 100644 Documentation/networking/siw.txt
>
> diff --git a/Documentation/networking/siw.txt
> b/Documentation/networking/siw.txt
> new file mode 100644
> index 0000000..805e21b
> --- /dev/null
> +++ b/Documentation/networking/siw.txt
> @@ -0,0 +1,156 @@
> +SoftiWARP: Software iWARP kernel driver module.
> +
> +General
> +-------
> +SoftiWARP (siw) implements the iWARP protocol suite (MPA/DDP/RDMAP,
> +IETF-RFC 5044/5041/5040) completely in software as a Linux kernel module.
> +siw runs on top of TCP kernel sockets and exports the Linux kernel ibverbs
> +RDMA interface. siw interfaces with the iwcm connection manager.
> +
> +
> +Transmit Path
> +-------------
> +If a send queue (SQ) work queue element gets posted, siw tries to send
> +it directly out of the application context. If the SQ was non-empty,
> +SQ processing is done asynchronously by a kernel worker thread. This
> +thread gets scheduled if the TCP socket signals new write space to
s/gets/is/
> +be available. If during send operation the socket send space becomes
> +exhausted, SQ processing is abandoned until new socket write space
> +becomes available.
> +
> +
> +Receive Path
> +------------
> +All application data is placed into target buffers within softirq
> +socket callback. Application notification is asynchronous.
> +
> +
> +User Interface
> +--------------
> +All user space fast path operations such as posting of work requests and
> +reaping of work completions currently involve a isynchronous call into
If you really mean "isynchronous", then it should be: an isynchronous call
but what is isynchronous?
> +the siw kernel module via ib_uverbs interface. Kernel/user-mapped send
> +and receive as well as completion queues are not part of the current code.
> +In particular, mapped completion queues may improve performance,
> +since reaping completion queue entries as well as re-arming
> +the completion queue could be done more efficiently.
> +
> +
> +Kernel Client Support
> +---------------------
> +To guarantee non-blocking fast path operations, for kernel clients
> +all work queue elements (send/receive/shared-receive queue) are
> +pre-allocated during connection resource setup.
> +
> +
> +Memory Management
> +-----------------
> +siw currently uses the ib_umem_get() function of the ib_core module
> +to pin memory for later use in data transfer operations. Transmit
> +and receive memory are checked against correct access permissions only
> +in the moment of access by the network input path or before pushing it
at the moment
> +to the TCP socket for transmission.
> +ib_umem_get() provides DMA mappings for the requested address space which
> +are not used by siw.
> +
> +
> +Module Parameters
> +-----------------
> +The following siw module parameters are recognized.
> +
> +loopback_enabled:
> + If set, siw attaches also to the looback device. Checked only
> + during module insertion.
> +
> +mpa_crc_required:
> + If set, the MPA CRC gets generated and checked both in tx and rx
s/gets/is/
> + path. Without hardware support, setting this flag will severely
> + hurt throughput. Default setting is 0 (off).
> +
> +mpa_crc_strict:
> + If set, MPA CRC will not be enabled, even if peer requests
> + it. If the peer requests CRC generation, the connection setup
> + will be aborted. Default setting is 1 (on).
> +
> +zcopy_tx:
> + If set, payload of non-signalled work requests
payloads ... are transferred
> + (such as non-signalled WRITE or SEND as well as all READ
> + responses) are transferred using the TCP sockets
> + sendpage interface. This parameter can be switched on and
> + off dynamically (echo 1 >> /sys/module/siw/parameters/zcopy_tx
> + for enablement, 0 for disabling). System load may benefits from
may benefit
> + using 0copy data transmission. 0copy is not enabled if
"0copy" is fugly (IMO).
> + mpa_crc_enabled is set. Default setting is 1 (on).
> +
> +tcp_nodelay:
> + If set, on the TCP socket the TCP_NODELAY option is set.
> + Default setting is 1 (on).
> +
> +iface_list:
> + Comma separated list of interfaces siw should attach to.
Comma-separated
> + If no list is given, siw attaches to all available devices.
> + If a list is given, siw skips those devices not listed.
> + Currently, the list is restricted to 12 entries. If needed,
> + the 'SIW_MAX_IF' #define in siw_main.c can be adaped.
adapted. ? (or modified)
> + This parameter might be usefull to skip devices which are
useful
> + attached to a real RNIC device. Default setting is an empty list.
> +
> +
> +Compile Time Flags:
> +-------------------
> +-DCHECK_DMA_CAPABILITIES
> + Checks if the device siw wants to attach to provides
> + DMA capabilities. While DMA capabilities are currently not
> + needed (siw works on top of a kernel TCP socket), siw
> + uses ib_umem_get() which performs a (not used) DMA address
> + translation. Writing a siw private memory reservation and
> + pinning routine would solve the issue.
> +
> +-DSIW_TX_FULLSEGS
> + Experimental, not enabled by default. If set,
> + siw tries not to overrun the socket (not sending until
> + -EAGAIN return), but stops sending if the current segment
> + would not fit into the socket's estimated tx buffer. With that,
> + wire FPDUs may get truncated by the TCP stack far less often.
> + Since this feature manipulates the sock's SOCK_NOSPACE
> + bit, it violates strict layering and is therefore considered
> + proprietary.
> + Since TCP is a byte stream protocol, no guarantee can be given
> + if FPDU's are not fragmented.
or FPDUs
> +
> +
> +Debugging SIW:
> +--------------
> +The siw_debug.h file defines a 'dprint' macro which is used to debug
> +siw at runtime. Verbosity of debugging is controlled at compile time
> +via setting the 'DPRINT_MASK' to a or'd list of know value as defined
to an or'd list of known value
> +in siw_debug.h, e.g. '#define DPRINT_MASK (DBG_ON|DBG_CM)' to debug
> +errors and connection management. Defining DPRINT_MASK to '0' avoids
> +to compile any runtime debugging code.
compiling any
> +
> +To track siw's useage of its objects (connection endpoints, tcp sockets,
usage
> +protection domains, queue pairs, shared receive queues, completion queues,
> +memory registrations, work queue elements), the /sys/class/infiniband/siw*
> +directory contains siw interface specific objects, which can be read to
> +gather simple statistics:
> +
> +/sys/class/infiniband/siw*/stats:
> + Summary of allocated WQE's, PD's, QP's, CQ's, SRQ's, MR's, CEP's.
All of those single quote/apostrophe marks are not needed.
> + WQE statistics are not gathered if 'DPRINT_MASK' is set to '0'
> + (see above).
> +
> +/sys/class/infiniband/siw*/qp:
> + Summary of allocated queue pairs. If queue pairs are allocated,
> + after reading 'qp' a more detailed status of all queue pairs has
> + been printed to the kernel syslog and can be retrieved via
> + 'dmesg' command.
> +
> +/sys/class/infiniband/siw*/cep:
> + Summary of allocated connection end points. If connection endpoints
> + are allocated, after reading 'cep' a more detailed status of all
> + CEP's is printed to the kernel syslog and can be retrieved via
ditto
> + 'dmesg' command.
> +
> +Using the sysfs to gather siw's object allocations is considered a
> +tentative aid during further driver development and should disappear
> +in a stable version of siw.
> --
HTH.
---
~Randy
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