On 08/26/2014 03:13 PM, Ola Liljedahl wrote:
Possibly we are missing a public API for looking up a queue (or
perhaps specifically an IPC queue) by name.
If you have two threads (in same or different processes) that first
try to look up an (IPC or global) queue by name and if this fails then
creates said IPC queue, you have introduced a race condition. Possibly
the second IPC queue create will fail because the named queue exists
(EEXIST) and the caller can then understand it does not have to create
the queue.
So I think we have some synchronization issues to understand and solve
when it comes to IPC. Because the primary use case for IPC will be for
communication between different programs (processes) so they have no
means for synchronization (I would rather not have to use other Linux
mechanisms for setting up an IPC channel).
Ola, I agree with that. We have function to look up for pool, but don't
have that function to loop up for queue. But it might be common case
where different threads want to reference to single queue.
odp_queue_t odp_queue_lookup(const char *name, odp_queue_type_t type)
which will do:
- walk over queue_tbl and compare name with argument, if name match
return it;
- if type ipc, search for shared memory object, if it's exist connect to it.
Maxim.
On 26 August 2014 11:48, Maxim Uvarov <maxim.uva...@linaro.org
<mailto:maxim.uva...@linaro.org>> wrote:
On 08/26/2014 12:56 PM, Taras Kondratiuk wrote:
On 08/25/2014 05:37 PM, Maxim Uvarov wrote:
I pushed here some raw code:
https://git.linaro.org/people/maxim.uvarov/odp.git/shortlog/refs/heads/odp_ipc2
Example here app here:
https://git.linaro.org/people/maxim.uvarov/odp.git/blob/refs/heads/odp_ipc2:/example/fork/odp_fork.c
pktio_queue_thread() takes packets from inq queue and put
them to ipc
queue.
ring_thread() takes packets from ipc queue and free this
buffer.
I have a few things I didn't understand:
1. It is not clear how IPC pktio and its pool is used.
Especially on
'sender' side.
We create pool somewhere. Then do loop up for it:
pkt_pool = odp_buffer_pool_lookup("packet_pool");
Then we want that IPC queue can work with that pool. So we open
pktio:
pktio_ipc_params.type = ODP_PKTIO_TYPE_IPC;
pktio_ipc = odp_pktio_open(NULL, pkt_pool, &pktio_ipc_params);
And then create queue:
ipcq_def = odp_queue_create("shared-queue", ODP_QUEUE_TYPE_IPC,
&qparam);
when we place packet to this queue with:
odp_queue_enq(ipcq_def, buf);
Than everything depend on implementation. So linux-generic
(software), packet data
still will be in pool. odp_buffer_t (uint32_t) value will be added
to ring.
Other process gets odp_buffer_t, and find pointer to that buffer
(odp_buffer_hdr_t*).
On hw implementation you just place odp_buffer_t to the queue. And
if ipc queue has the same
pool than packet can be delivered to software. If there are
different pools, then packet should be
copied to ipc pool, and after that delivered to hardware.
The main goal here is we can say that ipc pool can be the same as
ingress pool or it can be different.
Depends on hw configuration.
2. On both sides IPC queue is created. My impression was that
it should
be looked up on one side via pktio or directly via queue name.
Is there way to ask hardware which queues were already created?
Actually I do look up, but it's hidden in implementation. Idea is
that if queue type is IPC,
then I do loop up if that queue already exist. If exist then I
connect to that queue. If it does
not exist - I create it.
static void queue_init(queue_entry_t *queue, const char *name,
odp_queue_type_t type, odp_queue_param_t *param)
case ODP_QUEUE_TYPE_IPC:
queue->s.r = odp_ring_lookup(name);
if (!queue->s.r)
{
printf("creating new odp ring: %s\n", name);
queue->s.r = odp_ring_create(name, RING_SIZE,
ODP_RING_SHM_PROC);
if (queue->s.r == NULL) {
ODP_ERR("ring create failed\n");
}
} else
printf("odp ring found!!!\n");
Because of we can say that several processes can connect to one
queue, there is no difference
which exactly process will create this queue. So my idea was to
stay with original odp_queue_create() app API.
Thanks,
Maxim.
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