TAO is increasingly being used to support high-performance distributed real-time and embedded (DRE) applications. DRE applications constitute an important class of distributed systems where predictability and efficiency are essential for success. This document describes how to configure TAO to enhance its throughput, scalability, and latency for a variety of applications. We also explain various ways to speedup the compilation of ACE+TAO and applications that use ACE+TAO.
As with most applications, including compilers, enabling optimizations can often introduce side-effects that may not be desirable for all use-cases. TAO's default configuration therefore emphasizes programming simplicity rather than top speed or scalability. Our goal is to assure that CORBA applications work correctly ``out-of-the-box,'' while also enabling developers to further optimize their CORBA applications to meet stringent performance requirements.
TAO's performance tuning philosophy reflects the fact that there are trade-offs between speed, size, scalability, and programming simplicity. For example, certain ORB configurations work well for a large number of clients, whereas others work better for a small number. Likewise, certain configurations minimize internal ORB synchronization and memory allocation overhead by making assumptions about how applications are designed.
This document is organized as follows:
In this context, ``throughput'' refers to the number of events occurring per unit time, where ``events'' can refer to ORB-mediated operation invocations, for example. This section describes how to optimize client and server throughput.
It is important to understand that enabling throughput optimizations for the client may not affect the server performance and vice versa. In particular, the client and server ORBs may be designed by different ORB suppliers.
Client ORB throughput optimizations improve the rate at which CORBA requests (operation invocations) are sent to the target server. Depending on the application, various techniques can be employed to improve the rate at which CORBA requests are sent and/or the amount of work the client can perform as requests are sent or replies received. These techniques consist of:
We explore these techniques below.
For two-way invocations, i.e., those that expect a reply
(including ``void'' replies), Asynchronous method
invocations (AMI) can be used to give the client the opportunity
to perform other work as a CORBA request is sent to the target,
handled by the target, and the reply is received.
A TAO client ORB can be optimized for various types of applications:
A single-threaded client application may not require
the internal thread synchronization performed by TAO.
It may therefore be useful to add the following line to your
svc.conf file:
static Client_Strategy_Factory "-ORBProfileLock null"
If such an entry already exists in your
svc.conf file, then just add
-ORBProfileLock null to the list options
between the quotes found after
Client_Strategy_Factory.
Other options include disabling synchronization in the components of TAO responsible for constructing and sending requests to the target and for receiving replies. These components are called ``connection handlers.'' To disable synchronization in the client connection handlers, simply add:
-ORBClientConnectionHandler ST
to the list of Client_Strategy_Factory
options. Other values for this option, such as
RW, are more appropriate for "pure"
synchronous clients. See the
-ORBClientConnectionHandler option
documentation for details.
Clients with lower scalability requirements can dedicate a
connection to one request at a time, which means that no
other requests or replies will be sent or received,
respectively, over that connection while a request is
pending. The connection is exclusive to a given
request, thus reducing contention on a connection.
However, that exclusivity
comes at the cost of a smaller number of requests that
may be issued at a given point in time.
To enable this
behaviour, add the following option to the
Client_Strategy_Factory line of your
svc.conf file:
-ORBTransportMuxStrategy EXCLUSIVE
Throughput on the server side can be improved by configuring TAO
to use a thread-per-connection concurrency model. With
this concurrency model, a single thread is assigned to service
each connection. That same thread is used to dispatch the
request to the appropriate servant, meaning that thread context
switching is kept to minimum. To enable this concurrency model
in TAO, add the following option to the
Server_Strategy_Factory
entry in your svc.conf file:
-ORBConcurrency thread-per-connection
While the thread-per-connection concurrency model may
improve throughput, it generally does not scale well due to
limitations of the platform the application is running. In
particular, most operating systems cannot efficiently handle
more than 100 or 200 threads running
concurrently. Hence performance often degrades sharply as the
number of connections increases over those numbers.
Other concurrency models are further discussed in the Optimizing Server Scalability section below.
In this context, ``scalability'' refers to how well an ORB
performs as the number of CORBA requests increases. For
example, a non-scalable configuration will perform poorly as the
number of pending CORBA requests on the client increases from
10 to 1,000, and similarly on the
server. ORB scalability is particularly important on the server
since it must often handle many requests from multiple clients.
In order to optimize TAO for scalability on the client side,
connection multiplexing must be enabled. Specifically, multiple
requests may be issued and pending over the same connection.
Sharing a connection in this manner reduces the amount of
resources required by the ORB, which in turn makes more
resources available to the application. To enable this behavior
use the following Client_Strategy_Factory option:
-ORBTransportMuxStrategy MUXED
This is the default setting used by TAO.
Scalability on the server side depends greatly on the concurrency model in use. TAO supports two concurrency models:
The thread-per-connection concurrency model is described above in the Optimizing Server Throughput section.
A reactive concurrency model employs the Reactor design
pattern to demultiplex incoming CORBA requests. The underlying
event demultiplexing mechanism is typically one of the
mechanisms provided by the operating system, such as the
select(2) system call. To enable this concurrency
model, add the following option to the
Server_Strategy_Factory
entry in your svc.conf file:
-ORBConcurrency reactive
This is the default setting used by TAO.
The reactive concurrency model provides improved scalability on the server side due to the fact that less resources are used, which in turn allows a very large number of requests to be handled by the server side ORB. This concurrency model provides much better scalability than the thread-per-connection model described above.
Further scalability tuning can be achieved by choosing a Reactor
appropriate for your application. For example, if your
application is single-threaded then a reactor optimized for
single-threaded use may be appropriate. To select a
single-threaded select(2) based reactor, add the
following option to the
Advanced_Resource_Factory
entry in your svc.conf file:
-ORBReactorType select_st
If your application uses thread pools, then the thread pool reactor may be a better choice. To use it, add the following option instead:
-ORBReactorType tp_reactor
This is TAO's default reactor. See the
-ORBReactorType
documentation for other reactor choices.
Note that may have to link the TAO_Strategies
library into your application in order to take advantage of the
Advanced_Resource_Factory
features, such as alternate reactor choices.
A third concurrency model, unsupported by TAO, is thread-per-request. In this case, a single thread is used to service each request as it arrives. This concurrency model generally provides neither scalability nor speed, which is the reason why it is often not used in practice.
Disabling optimization for your application will come at the cost of run time performance, so you should normally only do this during development, keeping your test and release build optimized.
In order for code built with -DACE_NO_INLINE to link, you will need to be using a version of ACE+TAO built with the "inline=0" make flag.
In order to accommodate both inline and non-inline builds of your application it will be necessary to build two copies of your ACE+TAO libraries, one with inlining and one without. You can then use your ACE_ROOT and TAO_ROOT variables to point at the appropriate installation.
Ossama Othman Last modified: Wed Dec 25 06:23:55 CST 2002