On 19 May 2015 at 19:04, Benoît Ganne <[email protected]> wrote:
> Hi Ola,
>
> Thanks for sharing this. We are also looking at IPC at Kalray, where our ODP
> model is multi-process, shared-nothing, architecture.
> From our point of view, the main requirements for IPC would be:
> - use it to communicate between different address spaces (AS), and as such
> our messages should be bigger than just a pointer to a shared mem area
I agree. The data must be contained in the message.
> - use it for control/data planes signaling but also to exchange packets to
> be allowed to build packets processing pipelines
Control/data plane signaling must be reliable (per the definition in
my RFC). But do you have the same requirements for packet transfer
between pipeline stages (on different cores)? Or it just happens to be
reliable on your hardware? Is reliability (guaranteed delivery) an
inherent requirement for pipelined packet processing? (this would be
contrary to my experience).
Also couldn't you use ODP queues as the abstraction for transferring
packets between cores/pipeline stages? Per your pktio proposal below,
if you connect input and output queues to your "ipc" pktio instances,
applications can just enqueue and dequeue packets from these queues
and that will cause packets to be transferred between pipeline stages
(on different cores/AS's). This use case does not want or need the
ability to specify the destination address for each individual send
operation and this would likely just add overhead to a performance
critical operation.
Queues also support enqueueing of all types of events while my
proposed IPC mechanism only supports a new message event type.
> - IPC ops should be mapped to our NoC HW as much as possible, especially
> for send/recv operations
Is there anything in the proposed API that would limit your
implementation freedom?
>
> From your proposal, it seems to me that what you proposed is more like an
> application messaging bus such as d-bus (especially the deferred lookup()
> and monitor()),
Perhaps d-bus can be used as the implementation, that could save me
some work. But the IPC mechanism is extremely inspired by the OSE
(application) message passing mechanism (there was a borked attempt to
adapt OSE message passing to passing packets between pipeline stages
which showed why message passing and packet passing should not be
mixed).
> with a centralized rendez-vous point for resource
> management. It is certainly useful, especially for control/data plane
> signaling, but I would like to have a more low-level IPC mechanism, on top
> of which we could build this sort of messaging bus.
I proposed an API for the functionality I need. How each platform
implements it is up to them. Why would you want to expose a lower
level API? How would such an API look like and how would you implement
the functionality in my proposal? Would the low level API be
independent of the underlying platform?
>
> For this kind of lower-level mechanism I think pktio might be a good match.
My prototyping started out by tweaking the linux-generic packet_io
implementation. By specifying a special pktio interface name, the IPC
endpoint would be created. An Ethernet-like packet format (48-bit
destination and source address, 32 bit message type) was be used for
messages. The packet.h API would be used for accessing and
manipulating messages (which are of the packet event type). This is
still a potential implementation for Linux generic but a little bit
too close the packet semantics (unreliable transfer, segmented buffers
etc) for my intended use case. But messages are not packets and
reliable transfer is important.
> But in that case you need to be able to identify the endpoints. What I
> proposed in precedent thread, was to use a hierarchical device naming:
> - "/dev/<device>" for real devices
> - "/ipc/<identifier>" for IPC
> What I had in mind so far for our platform was to used {AS identifier + pool
> name in the AS} as IPC identifier, which would avoid the need of a
> centralized rendez-vous point.
The semantics of the IPC endpoint names are not defined in my
proposal. I think it is a mistake to impose meaning on the names. I
expect names to identify applications but an IPC name can identify
anything. Example and real applications will likely impose some kind
of structure on and meaning to names. But it is probably not a good
idea that the platform imposes meaning to IPC names (e.g. names
represent SoC topology), I can imagine how this will complicate
portability. pktio names however are already platform specific.
Also I don't envision any (active) rendez-vous point, it's just a
global shared table in my implementation for linux-generic. This is
needed since names are user-defined and arbitrary.
>
> Another slightly different subject is that we would like to extend pktio
> (but it is a common requirement for IPC) to be able to open pktio for
> read-only, write-only or read-write operations. This is because opening
> communications on our HW allocate HW resources for each configured RX (you
> need DMA endpoints to be configured). Being able to open write-only pktio
> help to save those resources, and would make sense even in the standard
> pktio.
>
> How could it look like? Here are some examples:
> - to open a read-only pktio in AS0:
> odp_pool_t local_pool = odp_pool_create("AS0_pool", ...);
> odp_pktio_open("/ipc/local", local_pool);
> Notes: "/ipc/local" identifies a local, read-only ipc endpoints.
> - to open a write-only pktio in AS1 to send data to AS0:
> odp_pktio_open("/ipc/AS0/AS0_pool", NULL);
Why are these pktio instances of type IPC? They could just as well be
network interfaces on which you send and/or receive packets with the
normal semantics. No need for the IPC API I proposed. What stops you
from implementing this today?
> Notes: "/ipc/AS0/AS0_pool" identifies a remote endpoints for writing:
> "AS0" identifies the address space, whereas "AS0_pool" identifies the packet
> pool in AS0 address space. The fact that we do not associate any default
> pool with pktio means it is write-only.
So we need to amend the API spec that it is OK to specify
ODP_POOL_INVALID for the pool parameter to the opd_pktio_open() call
and this will indicate that the pktio interface is write-only. Is
there anything similar we need to do for read-only interfaces? You
would like to have the indication of read-only/write-only/read-write
at the time of pktio_open. Perhaps we need a new parameter for
odp_pktio_open(), the pool parameter is not enough for this purpose.
Your needs are real but I think reusing the ODP pktio concept is a
better solution for you, not trying to hijack the application
messaging API which is intended for a very different use case. IPC
seems to mean different things to different people so perhaps should
be avoided in order not to give people the wrong ideas.
> - to open a read-write pktio between AS0 and AS1 in AS1:
> odp_pool_t local_pool = odp_pool_create("AS1_pool", ...);
> odp_pktio_open("/AS0/AS0_pool", local_pool);
>
> Thanks,
> ben
>
>
> On 05/19/2015 12:03 AM, Ola Liljedahl wrote:
>>
>> As promised, here is my first attempt at a standalone API for IPC - inter
>> process communication in a shared nothing architecture (message passing
>> between processes which do not share memory).
>>
>> Currently all definitions are in the file ipc.h but it is possible to
>> break out some message/event related definitions (everything from
>> odp_ipc_sender) in a separate file message.h. This would mimic the
>> packet_io.h/packet.h separation.
>>
>> The semantics of message passing is that sending a message to an endpoint
>> will always look like it succeeds. The appearance of endpoints is
>> explicitly
>> notified through user-defined messages specified in the odp_ipc_resolve()
>> call. Similarly, the disappearance (e.g. death or otherwise lost
>> connection)
>> is also explicitly notified through user-defined messages specified in the
>> odp_ipc_monitor() call. The send call does not fail because the addressed
>> endpoints has disappeared.
>>
>> Messages (from endpoint A to endpoint B) are delivered in order. If
>> message
>> N sent to an endpoint is delivered, then all messages <N have also been
>> delivered. Message delivery does not guarantee actual processing by the
>> recipient. End-to-end acknowledgements (using messages) should be used if
>> this guarantee is important to the user.
>>
>> IPC endpoints can be seen as interfaces (taps) to an internal reliable
>> multidrop network where each endpoint has a unique address which is only
>> valid for the lifetime of the endpoint. I.e. if an endpoint is destroyed
>> and then recreated (with the same name), the new endpoint will have a
>> new address (eventually endpoints addresses will have to be recycled but
>> not for a very long time). Endpoints names do not necessarily have to be
>> unique.
>>
>> Signed-off-by: Ola Liljedahl <[email protected]>
>> ---
>> (This document/code contribution attached is provided under the terms of
>> agreement LES-LTM-21309)
>>
>> include/odp/api/ipc.h | 261
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 261 insertions(+)
>> create mode 100644 include/odp/api/ipc.h
>>
>> diff --git a/include/odp/api/ipc.h b/include/odp/api/ipc.h
>> new file mode 100644
>> index 0000000..3395a34
>> --- /dev/null
>> +++ b/include/odp/api/ipc.h
>> @@ -0,0 +1,261 @@
>> +/* Copyright (c) 2015, Linaro Limited
>> + * All rights reserved.
>> + *
>> + * SPDX-License-Identifier: BSD-3-Clause
>> + */
>> +
>> +
>> +/**
>> + * @file
>> + *
>> + * ODP IPC API
>> + */
>> +
>> +#ifndef ODP_API_IPC_H_
>> +#define ODP_API_IPC_H_
>> +
>> +#ifdef __cplusplus
>> +extern "C" {
>> +#endif
>> +
>> +/** @defgroup odp_ipc ODP IPC
>> + * @{
>> + */
>> +
>> +/**
>> + * @typedef odp_ipc_t
>> + * ODP IPC handle
>> + */
>> +
>> +/**
>> + * @typedef odp_ipc_msg_t
>> + * ODP IPC message handle
>> + */
>> +
>> +
>> +/**
>> + * @def ODP_IPC_ADDR_SIZE
>> + * Size of the address of an IPC endpoint
>> + */
>> +
>> +/**
>> + * Create IPC endpoint
>> + *
>> + * @param name Name of local IPC endpoint
>> + * @param pool Pool for incoming messages
>> + *
>> + * @return IPC handle on success
>> + * @retval ODP_IPC_INVALID on failure and errno set
>> + */
>> +odp_ipc_t odp_ipc_create(const char *name, odp_pool_t pool);
>> +
>> +/**
>> + * Destroy IPC endpoint
>> + *
>> + * @param ipc IPC handle
>> + *
>> + * @retval 0 on success
>> + * @retval <0 on failure
>> + */
>> +int odp_ipc_destroy(odp_ipc_t ipc);
>> +
>> +/**
>> + * Set the default input queue for an IPC endpoint
>> + *
>> + * @param ipc IPC handle
>> + * @param queue Queue handle
>> + *
>> + * @retval 0 on success
>> + * @retval <0 on failure
>> + */
>> +int odp_ipc_inq_setdef(odp_ipc_t ipc, odp_queue_t queue);
>> +
>> +/**
>> + * Remove the default input queue
>> + *
>> + * Remove (disassociate) the default input queue from an IPC endpoint.
>> + * The queue itself is not touched.
>> + *
>> + * @param ipc IPC handle
>> + *
>> + * @retval 0 on success
>> + * @retval <0 on failure
>> + */
>> +int odp_ipc_inq_remdef(odp_ipc_t ipc);
>> +
>> +/**
>> + * Resolve endpoint by name
>> + *
>> + * Look up an existing or future endpoint by name.
>> + * When the endpoint exists, return the specified message with the
>> endpoint
>> + * as the sender.
>> + *
>> + * @param ipc IPC handle
>> + * @param name Name to resolve
>> + * @param msg Message to return
>> + */
>> +void odp_ipc_resolve(odp_ipc_t ipc,
>> + const char *name,
>> + odp_ipc_msg_t msg);
>> +
>> +/**
>> + * Monitor endpoint
>> + *
>> + * Monitor an existing (potentially already dead) endpoint.
>> + * When the endpoint is dead, return the specified message with the
>> endpoint
>> + * as the sender.
>> + *
>> + * Unrecognized or invalid endpoint addresses are treated as dead
>> endpoints.
>> + *
>> + * @param ipc IPC handle
>> + * @param addr Address of monitored endpoint
>> + * @param msg Message to return
>> + */
>> +void odp_ipc_monitor(odp_ipc_t ipc,
>> + const uint8_t addr[ODP_IPC_ADDR_SIZE],
>> + odp_ipc_msg_t msg);
>> +
>> +/**
>> + * Send message
>> + *
>> + * Send a message to an endpoint (which may already be dead).
>> + * Message delivery is ordered and reliable. All (accepted) messages will
>> be
>> + * delivered up to the point of endpoint death or lost connection.
>> + * Actual reception and processing is not guaranteed (use end-to-end
>> + * acknowledgements for that).
>> + * Monitor the remote endpoint to detect death or lost connection.
>> + *
>> + * @param ipc IPC handle
>> + * @param msg Message to send
>> + * @param addr Address of remote endpoint
>> + *
>> + * @retval 0 on success
>> + * @retval <0 on error
>> + */
>> +int odp_ipc_send(odp_ipc_t ipc,
>> + odp_ipc_msg_t msg,
>> + const uint8_t addr[ODP_IPC_ADDR_SIZE]);
>> +
>> +/**
>> + * Get address of sender (source) of message
>> + *
>> + * @param msg Message handle
>> + * @param addr Address of sender endpoint
>> + */
>> +void odp_ipc_sender(odp_ipc_msg_t msg,
>> + uint8_t addr[ODP_IPC_ADDR_SIZE]);
>> +
>> +/**
>> + * Message data pointer
>> + *
>> + * Return a pointer to the message data
>> + *
>> + * @param msg Message handle
>> + *
>> + * @return Pointer to the message data
>> + */
>> +void *odp_ipc_data(odp_ipc_msg_t msg);
>> +
>> +/**
>> + * Message data length
>> + *
>> + * Return length of the message data.
>> + *
>> + * @param msg Message handle
>> + *
>> + * @return Message length
>> + */
>> +uint32_t odp_ipc_length(const odp_ipc_msg_t msg);
>> +
>> +/**
>> + * Set message length
>> + *
>> + * Set length of the message data.
>> + *
>> + * @param msg Message handle
>> + * @param len New length
>> + *
>> + * @retval 0 on success
>> + * @retval <0 on error
>> + */
>> +int odp_ipc_reset(const odp_ipc_msg_t msg, uint32_t len);
>> +
>> +/**
>> + * Allocate message
>> + *
>> + * Allocate a message of a specific size.
>> + *
>> + * @param pool Message pool to allocate message from
>> + * @param len Length of the allocated message
>> + *
>> + * @return IPC message handle on success
>> + * @retval ODP_IPC_MSG_INVALID on failure and errno set
>> + */
>> +odp_ipc_msg_t odp_ipc_alloc(odp_pool_t pool, uint32_t len);
>> +
>> +/**
>> + * Free message
>> + *
>> + * Free message back to the message pool it was allocated from.
>> + *
>> + * @param msg Handle of message to free
>> + */
>> +void odp_ipc_free(odp_ipc_msg_t msg);
>> +
>> +/**
>> + * Get message handle from event
>> + *
>> + * Converts an ODP_EVENT_MESSAGE type event to a message.
>> + *
>> + * @param ev Event handle
>> + *
>> + * @return Message handle
>> + *
>> + * @see odp_event_type()
>> + */
>> +odp_ipc_msg_t odp_message_from_event(odp_event_t ev);
>> +
>> +/**
>> + * Convert message handle to event
>> + *
>> + * @param msg Message handle
>> + *
>> + * @return Event handle
>> + */
>> +odp_event_t odp_message_to_event(odp_ipc_msg_t msg);
>> +
>> +/**
>> + * Get printable value for an odp_ipc_t
>> + *
>> + * @param ipc IPC handle to be printed
>> + * @return uint64_t value that can be used to print/display this
>> + * handle
>> + *
>> + * @note This routine is intended to be used for diagnostic purposes
>> + * to enable applications to generate a printable value that represents
>> + * an odp_ipc_t handle.
>> + */
>> +uint64_t odp_ipc_to_u64(odp_ipc_t ipc);
>> +
>> +/**
>> + * Get printable value for an odp_ipc_msg_t
>> + *
>> + * @param msg Message handle to be printed
>> + * @return uint64_t value that can be used to print/display this
>> + * handle
>> + *
>> + * @note This routine is intended to be used for diagnostic purposes
>> + * to enable applications to generate a printable value that represents
>> + * an odp_ipc_msg_t handle.
>> + */
>> +uint64_t odp_ipc_msg_to_u64(odp_ipc_msg_t msg);
>> +
>> +/**
>> + * @}
>> + */
>> +
>> +#ifdef __cplusplus
>> +}
>> +#endif
>> +
>> +#endif
>>
>
>
> --
> Benoît GANNE
> Field Application Engineer, Kalray
> +33 (0)648 125 843
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