From 552e46339939933ee7ed305f1dda82ead362ece9 Mon Sep 17 00:00:00 2001 From: Christophe Milard Date: Thu, 24 Nov 2016 17:22:33 +0100 Subject: doc: updating docs for the shm interface extension Signed-off-by: Christophe Milard Reviewed-and-tested-by: Bill Fischofer Signed-off-by: Maxim Uvarov --- doc/users-guide/users-guide.adoc | 68 ++++++++++++++++++++++++++++++++++++++-- 1 file changed, 66 insertions(+), 2 deletions(-) (limited to 'doc') diff --git a/doc/users-guide/users-guide.adoc b/doc/users-guide/users-guide.adoc index 62f58336d..078dd7ccc 100755 --- a/doc/users-guide/users-guide.adoc +++ b/doc/users-guide/users-guide.adoc @@ -649,13 +649,19 @@ mapping the shared memory block. There is no fragmentation. By default ODP threads are assumed to behave as cache coherent systems: Any change performed on a shared memory block is guaranteed to eventually become visible to other ODP threads sharing this memory block. -(this behaviour may be altered by flags to `odp_shm_reserve()` in the future). Nevertheless, there is no implicit memory barrier associated with any action on shared memories: *When* a change performed by an ODP thread becomes visible to another ODP thread is not known: An application using shared memory blocks has to use some memory barrier provided by ODP to guarantee shared data validity between ODP threads. +The virtual address at which a given memory block is mapped in different ODP +threads may differ from ODP thread to ODP thread, if ODP threads have separate +virtual spaces (for instance if ODP threads are implemented as processes). +However, the ODP_SHM_SINGLE_VA flag can be used at `odp_shm_reserve()` time +to guarantee address uniqueness in all ODP threads, regardless of their +implementation or creation time. + === Lookup by name As mentioned, shared memory handles can be sent from ODP threads to ODP threads using any IPC mechanism, and then the block address retrieved. @@ -698,9 +704,49 @@ if (odp_shm_free(shm) != 0) { } ---- +=== sharing memory with the external world +ODP provides ways of sharing memory with entities located outside +ODP instances: + +Sharing a block of memory with an external (non ODP) thread is achieved +by setting the ODP_SHM_PROC flag at `odp_shm_reserve()` time. +How the memory block is retrieved on the Operating System side is +implementation and Operating System dependent. + +Sharing a block of memory with an external ODP instance (running +on the same Operating System) is achieved +by setting the ODP_SHM_EXPORT flag at `odp_shm_reserve()` time. +A block of memory created with this flag in an ODP instance A, can be "mapped" +into a remote ODP instance B (on the same OS) by using the +`odp_shm_import()`, on ODP instance B: + +.sharing memory between ODP instances: instance A +[source,c] +---- +odp_shm_t shmA; +shmA = odp_shm_reserve("memoryA", size, 0, ODP_SHM_EXPORT); +---- + +.sharing memory between ODP instances: instance B +[source,c] +---- +odp_shm_t shmB; +odp_instance_t odpA; + +/* get ODP A instance handle by some OS method */ +odpA = ... + +/* get the shared memory exported by A: +shmB = odp_shm_import("memoryA", odpA, "memoryB", 0, 0); +---- + +Note that the handles shmA and shmB are scoped by each ODP instance +(you can not use them outside the ODP instance they belong to). +Also note that both ODP instances have to call `odp_shm_free()` when done. + === Memory creation flags The last argument to odp_shm_reserve() is a set of ORed flags. -Two flags are supported: +The following flags are supported: ==== ODP_SHM_PROC When this flag is given, the allocated shared memory will become visible @@ -710,6 +756,12 @@ will be able to access the memory using native (non ODP) OS calls such as Each ODP implementation should provide a description on exactly how this mapping should be done on that specific platform. +==== ODP_SHM_EXPORT +When this flag is given, the allocated shared memory will become visible +to other ODP instances running on the same OS. +Other ODP instances willing to see this exported memory should use the +`odp_shm_import()` ODP function. + ==== ODP_SHM_SW_ONLY This flag tells ODP that the shared memory will be used by the ODP application software only: no HW (such as DMA, or other accelerator) will ever @@ -719,6 +771,18 @@ implementation), except for `odp_shm_lookup()` and `odp_shm_free()`. ODP implementations may use this flag as a hint for performance optimization, or may as well ignore this flag. +==== ODP_SHM_SINGLE_VA +This flag is used to guarantee the uniqueness of the address at which +the shared memory is mapped: without this flag, a given memory block may be +mapped at different virtual addresses (assuming the target have virtual +addresses) by different ODP threads. This means that the value returned by +`odp_shm_addr()` would be different in different threads, in this case. +Setting this flag guarantees that all ODP threads sharing this memory +block will see it at the same address (`odp_shm_addr()` would return the +same value on all ODP threads, for a given memory block, in this case) +Note that ODP implementations may have restrictions of the amount of memory +which can be allocated with this flag. + == Queues Queues are the fundamental event sequencing mechanism provided by ODP and all ODP applications make use of them either explicitly or implicitly. Queues are -- cgit v1.2.3