[openib-general] QoS RFC
Eitan Zahavi
eitan at mellanox.co.il
Tue May 30 07:41:05 PDT 2006
Hi All
Please find the attached RFC describing how QoS policy support could be
implemented in the OpenFabrics stack.
Your comments are welcome.
Eitan
RFC: OpenFabrics Enhancements for QoS Support
===============================================
Authors: . Eitan Zahavi <eitan at mellanox.co.il>
Date: .... May 2006.
Revision: 0.1
Table of contents:
1. Overview
2. Architecture
3. Supported Policy
4. CMA functionality
5. IPoIB functionality
6. SDP functionality
7. SRP functionality
8. iSER functionality
9. OpenSM functionality
1. Overview
------------
Quality of Service requirements stem from the realization of I/O
consolidation
over IB network: As multiple applications and ULPs share the same
fabric, means
to control their use of the network resources are becoming a must. The
basic
need is to differentiate the service levels provided to different
traffic flows.
Such that a policy could be enforced and control each flow utilization
of the
fabric resources.
IBTA specification defined several hardware features and management
interfaces
to support QoS:
* Up to 15 Virtual Lanes (VL) could carry traffic in a non-blocking
manner
* Arbitration between traffic of different VL is performed by a 2
priority
levels weighted round robin arbiter. The arbiter is programmable with
a sequence of (VL, weight) pairs and maximal number of high priority
credits
to be processed before low priority is served
* Packets carry class of service marking in the range 0 to 15 in their
header SL field
* Each switch can map the incoming packet by its SL to a particular
output
VL based on programmable table VL=SL-to-VL-MAP(in-port, out-port, SL)
* The Subnet Administrator controls each communication flow parameters
by providing them as a response to Path Record query
The IB QoS features provide the means to implement a DiffServ like
architecture.
DiffServ architecture (IETF RFC2474 2475) is widely used today in highly
dynamic
fabrics.
This proposal provides the detailed functional definition for the
various
software elements that are required to enable a DiffServ like
architecture over
the OpenFabrics software stack.
2. Architecture
----------------
This proposal split the QoS functionality between the SM/SA, CMA and the
various
ULPS. We take the "chronology approach" to describe how the overall
system
works:
2.1. The network manager (human) provides a set of rules (policy) that
defines
how the network is being configured and how its resources are split to
different
QoS-Levels. The policy also define how to decide which QoS-Level each
application or ULP or service use.
2.2. The SM analyzes the provided policy to see if it is realizable and
performs
the necessary fabric setup. The SM may continuously monitor the policy
and adapt
to changes in it. Part of this policy defines the default QoS-Level of
each
partition. The SA is being enhanced to match the requested Source,
Destination,
TClass, Service-ID (and optionally SL and priority) against the policy.
So
clients (ULPs, programs) can obtain a policy enforced QoS. The SM is
also
enhanced to support setting up partitions with appropriate IPoIB
broadcast
group. This broadcast group carries its QoS attributes: TClass, SL, MTU
and
RATE.
2.3. IPoIB is being setup. IPoIB uses the SL, MTU and RATE available on
the
multicast group which forms the broadcast group of this partition.
2.4. MPI which provides non IB based connection management should be
configured
to run using hard coded SLs. It uses these SLs in every QP being opened.
2.5. ULPs that use CM interface (like SRP) should have their own
pre-assigned
Service-ID and use it while obtaining PathRecord for establishing their
connections. The SA receiving the PathRecord should match it against the
policy
and return the appropriate PathRecord including SL, MTU, RATE and
TClass.
2.6. ULPs and programs using CMA to establish RC connection should
provide the
CMA the target IP and Service-ID. Some of the ULPs might also provide
TClass
(E.g. for SDP sockets that are provided the TOS socket option). The CMA
should
then use the provided Service-ID and optional TClass and pass them in
the
PathRecord request. The resulting PathRecord should be used for
configuring the
connection QP.
PathRecord and MultiPathRecord enhancement for QoS:
As mentioned above the PathRecord and MultiPathRecord attributes should
be
enhanced to carry the Service-ID which is a 64bit value. Given the
existing
definition for these attributes we propose to use the following fields
for
Service-ID:
* For PathRecord: use the first 2 reserved fields whicg are 32bits each
(component masks 0x1 and 0x2). Component mask 1 should be used to
refer to the
merged Service-ID field
* For MultiPathRecord: use 2 reserved fields:
1. after the packet life (8 bits) which is component mask bit 0x10000
(17)
2. the field before SDGID1 (56 bits) which is component mask bit
0x200000 (22)
Once merged they should be selected using component mask bit 0x10000
(17)
A new capability bit should describe the SM QoS support in the SA class
port
info. This approach provides an easy migration path for existing access
layer
and ULPs by not introducing a new attribute.
3. Supported Policy
--------------------
The QoS policy supported by this proposal is divided into 4 sub
sections:
* Node Group: a set of HCAs, Routers or Switches that share the same
settings.
A node groups might be a partition defined by the partition manager
policy in
terms of GUIDs. Future implementations might provide support for
NodeDescription
based definition of node groups.
* Fabric Setup:
Defines how the SL2VL and VLArb tables should be setup. This policy
definition
assumes the computation of target behavior should be performed outside
of
OpenSM.
* QoS-Levels Definition:
This section defines the possible sets of parameters for QoS that a
client might
be mapped to. Each set holds: SL and optionally: Max MTU, Max Rate, Path
Bits
(in case LMC > 0 is used for QoS) and TClass.
* Matching Rules:
A list of rules that match an incoming PathRecord request to a
QoS-Level. The
rules are processed in order such as the first match is applied. Each
rule is
built out of set of match expressions which should all match for the
rule to
apply. The matching expressions are defined for the following fields
** SRC and DST to lists of node groups
** Service-ID to a list of Service-ID or Service-ID ranges
** TClass to a list of TClass values or ranges
XML style syntax is provided for the policy file. However, a strict BNF
format
(provided in section 8) should be used for parsing it.
<?xml version="1.0" encoding="ISO-8859-1"?>
<qos-policy>
<!-- Port Groups define sets of ports to be used later in the settings
-->
<port-groups>
<!-- using port GUIDs -->
<port-group> <name>Storage</name> <use>our SRP storage targets</use>
<port-guid>0x1000000000000001</port-guid>
<port-guid>0x1000000000000002</port-guid>
</port-group>
<!-- using names obtained by concatenation of first 2 words of
NodeDescription
and port number -->
<port-group> <name>Virtual Servers</name> <use>node desc and IB port
#</use>
<port-name>vs1/HCA-1/P1</port-name>
<port-name>vs3/HCA-1/P1</port-name>
<port-name>vs3/HCA-2/P1</port-name>
</port-group>
<!-- using partitions defined in the partition policy -->
<port-group> <name>Partition 1</name> <use>default settings</use>
<partition>Part1</partition>
</port-group>
<!-- using node types HCA|ROUTER|SWITCH -->
<port-group> <name>Routers</name> <use>all routers</use>
<node-type>ROUTER</node-type>
</port-group>
</port-groups>
<qos-setup>
<!-- define all types of SL2VL tables always have 16 VL entries -->
<sl2vl-tables>
<!-- scope defines the exact devices and in/out ports the tables
apply to
if the same port is matching several rules the last one applies -->
<sl2vl-scope> <group>Part1</group> <from>*</from> <to>*</to>
<sl2vl-table>0,1,2,3,4,5,6,7,8,9,10,11,12,13,14</sl2vl-table>
</sl2vl-scope>
<!-- "across" means the port just connected to the given group,
also the link across port 1 is probably supporting only 2 VLs -->
<sl2vl-scope> <across>Storage</across> <from>*</from> <to>1</to>
<sl2vl-table>0,1,1,1,1,1,1,1,1,1,1,1,1,1,1</sl2vl-table>
</sl2vl-scope>
<sl2vl-tables>
<!-- define all types of VLArb tables. The length of the tables should
match the physically supported tables by their target ports -->
<vlarb-tables>
<!-- scope defines the exact ports the VLArb tables apply to -->
<vlarb-scope> <group>Storage</group> <to>*</to>
<!-- VLArb table holds VL and weight pairs -->
<vlarb-high>0:255,1:127,2:63,3:31,4:15,5:7,6:3,7:1</vlarb-high>
<vlarb-low>8:255,9:127,10:63,11:31,12:15,13:7,14:3</vlarb-low>
<vl-high-limit>10</vl-high-limit>
</vlarb-scope>
</vlarb-tables>
</qos-setup>
<qos-levels>
<!-- the first one is just setting SL -->
<qos-level> <sn>1</sn> <use>for the lowest priority comm</use>
<sl>16</sl>
</qos-level>
<!-- the second sets SL and TClass -->
<qos-level> <sn>2</sn> <use>low latency best bandwidth</use>
<sl>0</sl> <tclass>7</tclass>
</qos-level>
<!-- the whole set: SL, TClass, MTU-Limit, Rate-Limit, Path-Bits -->
<qos-level> <sn>3</sn> <use>just an example</use>
<sl>0</sl> <tclass>32</tclass> <mtu_limit>1</mtl_limit>
<rate_limit>1</rate_limit>
</qos-level>
</qos-levels>
<qos_match_rules>
<!-- matching by single criteria: tclass (list of values and ranges)
-->
<qos_match_rule> <sn>1</sn> <use>low latency by tclass 7-9 or
11></use>
<tclass>7-9,11</tclass> <match-level>1</match-level>
</qos_match_rule>
<!-- show matching by destination group AND service-ids -->
<qos_match_rule> <sn>2</sn> <use>Storage targets connection></use>
<destination>Storage</destination> <service>22,4719</service>
<match-level>3</match-level>
</qos_match_rule>
</qos_match_rules>
</qos-policy>
4. IPoIB
---------
IPoIB already query the SA for its broadcast group information. The
additional
functionality required is for IPoIB to provide the broadcast group SL,
MTU, RATE
and TClass in every following PathRecord query performed when a new UDAV
is
needed by IPoIB.
We could assign a special Service-ID for IPoIB use but since all
communication
on the same IPoIB interface shares the same QoS-Level without the
ability to
differentiate it by target service we can ignore it for simplicity.
5. CMA features
----------------
The CMA interface supports Service-ID through the notion of port space
as a
prefixes to the port_num which is part of the sockaddr provided to
rdma_resolve_add(). What is missing is the explicit request for a TClass
that
should allow the ULP (like SDP) to propagate a specific request for a
class of
service. A mechanism for providing the TClass is available in the IPv6
address,
so we could use that address field. Another option is to implement a
special
connection options API for CMA.
Missing functionality by CMA is the usage of the provided TClass and
Service-ID
in the sent PathRecord. When a response is obtained it is an existing
requirement for the CMA to use the PathRecord from the response in
setting up
the QP address vector.
6. SDP
-------
SDP uses CMA for building its connections.
The Service-ID for SDP is 0x000000000001PPPP, where PPPP are 4 hex
digits
holding the remote TCP/IP Port Number to connect to.
SDP might be provided with SO_PRIORITY socket option. In that case the
value
provided should be sent to the CMA as the TClass option of that
connection.
7. SRP
-------
Current SRP implementation uses its own CM callbacks (not CMA). So SRP
should
fill in the Service-ID in the PathRecord by itself and use that
information in
setting up the QP. The T10 SRP standard defines the SRP Service-ID to be
defined
by the SRP target I/O Controller (but they should also comply with IBTA
Service-
ID rules). Anyway, the Service-ID is reported by the I/O Controller in
the
ServiceEntries DMA attribute and should be used in the PathRecord if the
SA
reports its ability to handle QoS PathRecords.
8. iSER
--------
iSER uses CMA and thus should be very close to SDP. The Service-ID for
iSER
should be TBD.
9. OpenSM features
-------------------
The QoS related functionality to be provided by OpenSM can be split into
two
main parts:
3.1. Fabric Setup
During fabric initialization the SM should parse the policy and apply
its
settings to the discovered fabric elements. The following actions should
be
performed:
* Parsing of policy
* Node Group identification. Warning should be provided for each node
not
specified but found.
* SL2VL settings validation should be checked:
+ A warning will be provided if there are no matching targets for the
SL2VL
setting statement.
+ An error message will be printed to the log file if an invalid
setting is
found. A setting is invalid if it refers to:
- Non existing port numbers of the target devices
- Unsupported VLs for the target device. In the later case the map
to non
existing VLs should be replaced to VL15 i.e. packets will be
dropped.
* SL2VL setting is to be performed
* VL Arbitration table settings should be validated according to the
following
rules:
+ A warning will be provided if there are no matching targets for the
setting
statement
+ An error will be provided if the port number exceeds the target
ports
+ An error will be generated if the table length exceeds device
capabilities
+ An warning will be generated if the table quote a VL that is not
supported
by the target device
* VL Arbitration tables will be set on the appropriate targets
3.2. PathRecord query handling:
OpenSM should be able to enforce the provided policy on client request.
The overall flow for such requests is: first the request is matched
against the
defined match rules such that the target QoS-Level definition is found.
Given
the QoS-Level a path(s) search is performed with the given restrictions
imposed
by that level. The following two sections describe these steps.
One issue not standardized by the IBTA is how Service-ID is carried in
the
PathRecord and MultiPathRecord attributes. There are basically two
options:
a. Replace the SM-Key field by the Service-ID. In that case no
component mask
bit will be assigned to it. Such that if the field is zero we should
treat it
as if the component mask bit is clear.
b. Encode it into spare fields. For PathRecord the first two fields are
reserved
and are 64 bit when combined. The first component mask bit maps to
the first
reserved field and should be used for Service-ID masking. For
MultiPathRecord
attribute there are no adjacent reserve fields that makes a 64 bit
field. So
the reserve field following the packet-lifetime (8 bits) combined
with the
reserved field DGIDCount (56 bits) can make the Service-ID. In this
case also
the first reserve field component mask bit should be used as the
Service-ID
component mask bit.
3.2.1. Matching rule search:
A rule is "matching" a PathRecord request using the following criteria:
* Matching rules provide values in a list of either single value, or
range of
values. A PathRecord field is "matching" the rule field if it is
explicitly
noted in the list of values or is one of the values covered by a range
included in the field values list.
* Only PathRecord fields that have their component mask bit set should
be
compared.
* For a rule to be "matching" a PathRecord request all the rule fields
should be
"matching" their PathRecord fields. Such that a PathRecord request
that does
not have a component mask field set for one of the rule defined fields
- can
not match that rule.
* A PathRecord request that have a component mask bit set for one of the
fields
that is not defined by the rule - can match the rule.
The algorithm to be used for searching for a rule match might be as
simple as a
sequential search through all rules or enhanced for better performance.
The
semantics of every rule field and its matching PathRecord field are
described
below:
* Source: the SGID or SLID should be part of this group
* Destination: the DGID or DLID should be part of this group
* Service-ID: check if the requested Service-ID (available in the
PathRecord old
SM-Key field) is matching any of this rule Service-IDs
* TClass: check if the PathRecord TClass field is matching
3.2.2 PathRecord response generation:
The QoS-Level pointed by the first rule that matches the PathRecord
request
should be used for obtaining the response SL, MTU-Limit, RATE-Limit,
Path-Bits
and TClass. A default QoS-Level should be used if no rule is matching
the query.
The efficient algorithm for finding paths that meet the QoS-Level
criteria is
beyond the scope of this RFC and left for the implementer to provide.
However
the criteria by which the paths match the QoS-Level are described below:
* SL: The paths found should all use the given SL. For that sake
PathRecord
algorithm should traverse the path from source to destination only
through
ports that carry a valid VL (not VL15) by the SL2VL map (should
consider input
and output ports and SL).
* MTU-Limit: The resulting paths MTU should not exceed the given
MTU-Limit
* Rate-Limit: The resulting paths RATE should not exceed the given
RATE-Limit
(rate limit is given in units of link BW = Width*Speed according to
IBTA
Specification Vol-1 table-205 p-901 l-24).
* Path-Bits: define the target LID lowest bits (number of bits defined
by the
target port PortInfo.LMC field). The path should traverse the LFT
using the
target port LID with the path-bits set.
* TClass: should be returned in the result PathRecord. When routing is
going to
be supported by OpenSM - we might use this field in selecting the
target
router too in a TBD way.
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