High-level feedback:
- An IB fabric could be used for a single ULP and still require QoS. The issue is how to differentiate flows on a given shared element within the fabric.
- QoS controls must be dynamic. The document references initialization as the time when decisions are made but obviously that is just a first pass on use of the fabric and not what it will become in potentially a short period of time.
- QoS also involves multi-path support (not really touched upon in terms of specifics in this document). Distributing or segregating work even if for the same ULP should be done across multiple or distinct paths. In one sense this may complicate the work but in another it is simpler in that arbitration controls for shared links become easier to manage if the number of flows is reduced.
- IP over IB defines a multicast group which is ultimately a spanning tree. That should not constrain what paths are used to communicate between endnode pairs. That only defines the multicast paths which are not strongly ordered relative to the unicast traffic. Further IP over IB may operate using the RC mode between endnodes. It is very simple to replicate RC and then segregate these into QoS domains (one could just align priority with the 802.1p for simplicity and practical execution) which can in turn flow over shared or distinct paths.
- IB is a centrally managed fabric. Adding in SID into records and such really isn't going to help solve the problem unless there is also a centralized management entity well above IB that can prioritize communication service rates for different ULP and endnode pairs. Given most of these centralized management entities are rather ignorant of IB at the moment, this presents a chicken-egg dilemma which is further complicated by developing SOA technology. It might be more valuable in one sense to examine SOA technology and how it is translating itself to say Ethernet and then see how this can be leveraged to IB.
- QoS needs to examine the sums of the consumers of a given path and their service rate requirements. It isn't just about setting a priority level but also about the packet injection rate to the fabric on that priority. This needs to be taken into account as well.
Overall, it is not clear to me what the end value of this document. The challenge for any network admin is to translate SOA driven requirements into fabric control knob setting. Without such translation algorithms / understanding, it is not clear that there is anything truly missing in the IBTA spec suite or that this RFC will really advance the integration of IB into the data center in a truly meaningful manner.
Mike
At 07:53 AM 5/30/2006, Eitan Zahavi wrote:
To: OPENIB <[email protected]>
Subject: QoS RFC - Resend using a friendly mailer
--text follows this line--
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 <[EMAIL PROTECTED]>
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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