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Add the LINKx provider man page. Signed-off-by: Amir Shehata <shehataa@ornl.gov>
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--- | ||
layout: page | ||
title: fi_lnx(7) | ||
tagline: Libfabric Programmer's Manual | ||
--- | ||
{% include JB/setup %} | ||
|
||
# NAME | ||
|
||
fi_lnx \- The LINKx Provider | ||
|
||
# OVERVIEW | ||
|
||
The LINKx provider is designed to link two or more providers, allowing | ||
applications to seamlessly use multiple providers or NICs. This provider uses | ||
the libfabric peer infrastructure to aid in the use of the underlying providers. | ||
This version of the provider currently supports linking the libfabric | ||
shared memory provider for intra-node traffic and another provider for | ||
inter-node traffic. Future releases of the provider will allow linking any | ||
number of providers and provide the users with the ability to influence | ||
the way the providers are utilized for traffic load. | ||
|
||
# SUPPORTED FEATURES | ||
|
||
This release contains an initial implementation of the LINKx provider that | ||
offers the following support: | ||
|
||
*Endpoint types* | ||
: The provider supports only endpoint type *FI_EP_RDM*. | ||
|
||
*Endpoint capabilities* | ||
: LINKx is a passthrough layer on the send path. On the receive path LINKx | ||
utilizes the peer infrastructure to create shared receive queues (SRQ). | ||
Receive requests are placed on the SRQ instead of on the core provider | ||
receive queue. When the provider receives a message it queries the SRQ for | ||
a match. If one is found the receive request is completed, otherwise the | ||
message is placed on the LINKx shared unexpected queue (SUQ). Further receive | ||
requests query the SUQ for matches. | ||
The first release of the provider only supports tagged and RMA operations. | ||
Other message types will be supported in future releases. | ||
|
||
*Modes* | ||
: The provider does not require the use of any mode bits. | ||
|
||
*Progress* | ||
: LINKx utilizes the peer infrastructure to provide a shared completion | ||
queue. Each linked provider still needs to handle its own progress. | ||
Completion events will however be placed on the shared completion queue, | ||
which is passed to the application for access. | ||
|
||
*Address Format* | ||
: LINKx wraps the linked providers addresses in one common binary blob. | ||
It does not alter or change the linked providers address format. It wraps | ||
them into a LINKx structure which is then flattened and returned to the | ||
application. This is passed between different nodes. The LINKx provider | ||
is able to parse the flattened format and operate on the different links. | ||
This assumes that nodes in the same group are all using the same version of | ||
the provider with the exact same links. IE: you can't have one node linking | ||
SHM+CXI while another linking SHM+RXM. | ||
|
||
*Message Operations* | ||
: LINKx is designed to intercept message operations such as fi_tsenddata | ||
and based on specific criteria forward the operation to the appropriate | ||
provider. For the first release, LINKx will only support linking SHM | ||
provider for intra-node traffic and another provider (ex: CXI) for inter | ||
node traffic. LINKx send operation looks at the destination and based on | ||
whether the destination is local or remote it will select the provider to | ||
forward the operation to. The receive case has been described earlier. | ||
|
||
*Using the Provider* | ||
: In order to use the provider the user needs to set FI_LINKX_PROV_LINKS | ||
environment variable to the linked providers in the following format | ||
shm+<prov>. This will allow LINKx to report back to the application in the | ||
fi_getinfo() call the different links which can be selected. Since there are | ||
multiple domains per provider LINKx reports a permutation of all the | ||
possible links. For example if there are two CXI interfaces on the machine | ||
LINKx will report back shm+cxi0 and shm+cxi1. The application can then | ||
select based on its own criteria the link it wishes to use. | ||
The application typically uses the PCI information in the fi_info | ||
structure to select the interface to use. A common selection criteria is | ||
the interface nearest the core the process is bound to. In order to make | ||
this determination, the application requires the PCI information about the | ||
interface. For this reason LINKx forwards the PCI information for the | ||
inter-node provider in the link to the application. | ||
|
||
# LIMITATIONS AND FUTURE WORK | ||
|
||
*Hardware Support* | ||
: LINKx doesn't support hardware offload; ex hardware tag matching. This is | ||
an inherit limitation when using the peer infrastructure. Due to the use | ||
of a shared receive queue which linked providers need to query when | ||
a message is received, any hardware offload which requires sending the | ||
receive buffers to the hardware directly will not work with the shared | ||
receive queue. The shared receive queue provides two advantages; 1) reduce | ||
memory usage, 2) coordinate the receive operations. For #2 this is needed | ||
when receiving from FI_ADDR_UNSPEC. In this case both providers which are | ||
part of the link can race to gain access to the receive buffer. It is | ||
a future effort to determine a way to use hardware tag matching and other | ||
hardware offload capability with LINKx | ||
|
||
*Limited Linking* | ||
: This release of the provider supports linking SHM provider for intra-node | ||
operations and another provider which supports the FI_PEER capability for | ||
inter-node operations. It is a future effort to expand to link any | ||
multiple sets of providers. | ||
|
||
*Memory Registration* | ||
: As part of the memory registration operation, varying hardware can perform | ||
hardware specific steps such as memory pinning. Due to the fact that | ||
memory registration APIs do not specify the source or destination | ||
addresses it is not possible for LINKx to determine which provider to | ||
forward the memory registration to. LINkx, therefore, registers the memory | ||
with all linked providers. This might not be efficient and might have | ||
unforeseen side effects. A better method is needed to support memory | ||
registration. | ||
|
||
*Operation Types* | ||
: This release of LINKx supports tagged and RMA operations only. Future | ||
releases will expand the support to other operation types. | ||
|
||
*Multi-Rail* | ||
: Future design effort is being planned to support utilizing multiple interfaces | ||
for traffic simultaneously. This can be over homogeneous interfaces or over | ||
heterogeneous interfaces. | ||
|
||
# RUNTIME PARAMETERS | ||
|
||
The *LINKx* provider checks for the following environment variables: | ||
|
||
*FI_LINKX_PROV_LINKS* | ||
: This environment variable is used to specify which providers to link. This | ||
must be set in order for the LINKx provider to return a list of fi_info | ||
blocks in the fi_getinfo() call. The format which must be used is: | ||
<prov1>+<prov2>+... As mentioned earlier currently LINKx supports linking | ||
only two providers the first of which is SHM followed by one other | ||
provider for inter-node operations | ||
|
||
*FI_LINKX_DISABLE_SHM* | ||
: By default this environment variable is set to 0. However, the user can | ||
set it to one and then the SHM provider will not be used. This can be | ||
useful for debugging and performance analysis. The SHM provider will | ||
naturally be used for all intra-node operations. Therefore, to test SHM in | ||
isolation with LINKx, the processes can be limited to the same node only. | ||
|
||
*FI_LINKX_SRQ_SUPPORT* | ||
: Shared Receive Queues are integral part of the peer infrastructure, but | ||
they have the limitation of not using hardware offload, such as tag | ||
matching. SRQ is needed to support the FI_ADDR_UNSPEC case. If the application | ||
is sure this will never be the case, then it can turn off SRQ support by | ||
setting this environment variable to 0. It is 1 by default. | ||
|
||
# SEE ALSO | ||
|
||
[`fabric`(7)](fabric.7.html), | ||
[`fi_provider`(7)](fi_provider.7.html), | ||
[`fi_getinfo`(3)](fi_getinfo.3.html) |
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.\" Automatically generated by Pandoc 2.9.2.1 | ||
.\" | ||
.TH "fi_lnx" "7" "" "" "" | ||
.hy | ||
.PP | ||
{% include JB/setup %} | ||
.SH NAME | ||
.PP | ||
fi_lnx - The LINKx Provider | ||
.SH OVERVIEW | ||
.PP | ||
The LINKx provider is designed to link two or more providers, allowing | ||
applications to seamlessly use multiple providers or NICs. | ||
This provider uses the libfabric peer infrastructure to aid in the use | ||
of the underlying providers. | ||
This version of the provider currently supports linking the libfabric | ||
shared memory provider for intra-node traffic and another provider for | ||
inter-node traffic. | ||
Future releases of the provider will allow linking any number of | ||
providers and provide the users with the ability to influence the way | ||
the providers are utilized for traffic load. | ||
.SH SUPPORTED FEATURES | ||
.PP | ||
This release contains an initial implementation of the LINKx provider | ||
that offers the following support: | ||
.TP | ||
\f[I]Endpoint types\f[R] | ||
The provider supports only endpoint type \f[I]FI_EP_RDM\f[R]. | ||
.TP | ||
\f[I]Endpoint capabilities\f[R] | ||
LINKx is a passthrough layer on the send path. | ||
On the receive path LINKx utilizes the peer infrastructure to create | ||
shared receive queues (SRQ). | ||
Receive requests are placed on the SRQ instead of on the core provider | ||
receive queue. | ||
When the provider receives a message it queries the SRQ for a match. | ||
If one is found the receive request is completed, otherwise the message | ||
is placed on the LINKx shared unexpected queue (SUQ). | ||
Further receive requests query the SUQ for matches. | ||
The first release of the provider only supports tagged and RMA | ||
operations. | ||
Other message types will be supported in future releases. | ||
.TP | ||
\f[I]Modes\f[R] | ||
The provider does not require the use of any mode bits. | ||
.TP | ||
\f[I]Progress\f[R] | ||
LINKx utilizes the peer infrastructure to provide a shared completion | ||
queue. | ||
Each linked provider still needs to handle its own progress. | ||
Completion events will however be placed on the shared completion queue, | ||
which is passed to the application for access. | ||
.TP | ||
\f[I]Address Format\f[R] | ||
LINKx wraps the linked providers addresses in one common binary blob. | ||
It does not alter or change the linked providers address format. | ||
It wraps them into a LINKx structure which is then flattened and | ||
returned to the application. | ||
This is passed between different nodes. | ||
The LINKx provider is able to parse the flattened format and operate on | ||
the different links. | ||
This assumes that nodes in the same group are all using the same version | ||
of the provider with the exact same links. | ||
IE: you can\[cq]t have one node linking SHM+CXI while another linking | ||
SHM+RXM. | ||
.TP | ||
\f[I]Message Operations\f[R] | ||
LINKx is designed to intercept message operations such as fi_tsenddata | ||
and based on specific criteria forward the operation to the appropriate | ||
provider. | ||
For the first release, LINKx will only support linking SHM provider for | ||
intra-node traffic and another provider (ex: CXI) for inter node | ||
traffic. | ||
LINKx send operation looks at the destination and based on whether the | ||
destination is local or remote it will select the provider to forward | ||
the operation to. | ||
The receive case has been described earlier. | ||
.TP | ||
\f[I]Using the Provider\f[R] | ||
In order to use the provider the user needs to set FI_LINKX_PROV_LINKS | ||
environment variable to the linked providers in the following format | ||
shm+. | ||
This will allow LINKx to report back to the application in the | ||
fi_getinfo() call the different links which can be selected. | ||
Since there are multiple domains per provider LINKx reports a | ||
permutation of all the possible links. | ||
For example if there are two CXI interfaces on the machine LINKx will | ||
report back shm+cxi0 and shm+cxi1. | ||
The application can then select based on its own criteria the link it | ||
wishes to use. | ||
The application typically uses the PCI information in the fi_info | ||
structure to select the interface to use. | ||
A common selection criteria is the interface nearest the core the | ||
process is bound to. | ||
In order to make this determination, the application requires the PCI | ||
information about the interface. | ||
For this reason LINKx forwards the PCI information for the inter-node | ||
provider in the link to the application. | ||
.SH LIMITATIONS AND FUTURE WORK | ||
.TP | ||
\f[I]Hardware Support\f[R] | ||
LINKx doesn\[cq]t support hardware offload; ex hardware tag matching. | ||
This is an inherit limitation when using the peer infrastructure. | ||
Due to the use of a shared receive queue which linked providers need to | ||
query when a message is received, any hardware offload which requires | ||
sending the receive buffers to the hardware directly will not work with | ||
the shared receive queue. | ||
The shared receive queue provides two advantages; 1) reduce memory | ||
usage, 2) coordinate the receive operations. | ||
For #2 this is needed when receiving from FI_ADDR_UNSPEC. | ||
In this case both providers which are part of the link can race to gain | ||
access to the receive buffer. | ||
It is a future effort to determine a way to use hardware tag matching | ||
and other hardware offload capability with LINKx | ||
.TP | ||
\f[I]Limited Linking\f[R] | ||
This release of the provider supports linking SHM provider for | ||
intra-node operations and another provider which supports the FI_PEER | ||
capability for inter-node operations. | ||
It is a future effort to expand to link any multiple sets of providers. | ||
.TP | ||
\f[I]Memory Registration\f[R] | ||
As part of the memory registration operation, varying hardware can | ||
perform hardware specific steps such as memory pinning. | ||
Due to the fact that memory registration APIs do not specify the source | ||
or destination addresses it is not possible for LINKx to determine which | ||
provider to forward the memory registration to. | ||
LINkx, therefore, registers the memory with all linked providers. | ||
This might not be efficient and might have unforeseen side effects. | ||
A better method is needed to support memory registration. | ||
.TP | ||
\f[I]Operation Types\f[R] | ||
This release of LINKx supports tagged and RMA operations only. | ||
Future releases will expand the support to other operation types. | ||
.TP | ||
\f[I]Multi-Rail\f[R] | ||
Future design effort is being planned to support utilizing multiple | ||
interfaces for traffic simultaneously. | ||
This can be over homogeneous interfaces or over heterogeneous | ||
interfaces. | ||
.SH RUNTIME PARAMETERS | ||
.PP | ||
The \f[I]LINKx\f[R] provider checks for the following environment | ||
variables: | ||
.TP | ||
\f[I]FI_LINKX_PROV_LINKS\f[R] | ||
This environment variable is used to specify which providers to link. | ||
This must be set in order for the LINKx provider to return a list of | ||
fi_info blocks in the fi_getinfo() call. | ||
The format which must be used is: ++\&... As mentioned earlier currently | ||
LINKx supports linking only two providers the first of which is SHM | ||
followed by one other provider for inter-node operations | ||
.TP | ||
\f[I]FI_LINKX_DISABLE_SHM\f[R] | ||
By default this environment variable is set to 0. | ||
However, the user can set it to one and then the SHM provider will not | ||
be used. | ||
This can be useful for debugging and performance analysis. | ||
The SHM provider will naturally be used for all intra-node operations. | ||
Therefore, to test SHM in isolation with LINKx, the processes can be | ||
limited to the same node only. | ||
.TP | ||
\f[I]FI_LINKX_SRQ_SUPPORT\f[R] | ||
Shared Receive Queues are integral part of the peer infrastructure, but | ||
they have the limitation of not using hardware offload, such as tag | ||
matching. | ||
SRQ is needed to support the FI_ADDR_UNSPEC case. | ||
If the application is sure this will never be the case, then it can turn | ||
off SRQ support by setting this environment variable to 0. | ||
It is 1 by default. | ||
.SH SEE ALSO | ||
.PP | ||
\f[C]fabric\f[R](7), \f[C]fi_provider\f[R](7), \f[C]fi_getinfo\f[R](3) |