illumos: manual page: latencytop.8

LATENCYTOP(8) Maintenance Procedures LATENCYTOP(8)

NAME

latencytop - report latency-related statistics in system and in
applications

SYNOPSIS

latencytop [-t interval] [-o log_file] [-k log_level]
[-f [no]feature,...] [-l log_interval] [-h]

DESCRIPTION

LatencyTOP is an observability tool that reports statistics about
latencies in the system and in applications. The tool reports statistics
about where and what kind of latencies are happening in the system and in
the applications that are running on the system. The statistics then can
be used to improve performance throughput of applications and system, as
you remove the identified latencies.

The tool analyzes system activity periodically and displays the data in
the output window. Two types of latencies are tracked: an LWP going in
and out of sleep and an LWP spinning order to acquire a synchronization
object. The tool uses the Solaris DTrace framework to collect the
statistics corresponding to these two scenarios of inactivity of the
system and application LWPs.

The output window is divided into two sections. An upper part displays
the system-wide statistics, while the lower part displays statistics
about individual processes. The user can navigate the list of processes
(using the left- and right-arrow keys) and select the list they are
interested in. The tool will then display statistics about that selected
process in the lower part of the window. If the t or T key is pressed,
the tool displays the LWP-specific view of that selected process. The t
or T key can be used to toggle between the process-view and the thread-
view.

During execution, a user can force a refresh of the analysis by pressing
the r or R key. The interval time is restored to the default or to a
specified value (if -t was used). To quit the application, the user must
press the q or Q key.

OPTIONS

The following options are supported:

-f, --feature [no]feature1,[no]feature2,...

Enables/disables features in LatencyTOP. Features can be only one of
the following:

[no]filter

Filter large interruptible latencies, for example, sleep. The
default is off.

[no]sched

Monitors sched (PID=0). The default is off.

[no]sobj

Monitors synchronize objects. The default is on.

[no]low

Lower overhead by sampling small latencies. Enabling this feature
will lower CPU utilization by estimating small latencies
statistically. Use it for heavy workloads such as a very busy web
server. The default is off.

-h

Displays the command's usage.

-k log_level

Specifies the level of logging in the log file. Valid values are:

0
none (default)

1
unknown

2
all

-l [log_interval]

Writes data to the log file every log_interval seconds; log_interval
must be greater than 60.

-o log_file

Specifies the log file where output will be written. The default log
file is /var/log/latencytop.log.

-t interval

Specifies the interval, in seconds, at which the tool collects
statistics from the system. The possible values are between 1 and 60;
the default is 5 seconds.

EXAMPLES

Example 1: Running the Tool

The following command launches the tool with default values for options.

% latencytop

Example 2: Setting the Interval

The following command sets the sampling interval to two seconds.

% latencytop -t 2

Example 3: Specifying the Log File

The following command sets the log file to /tmp/latencytop.log.

% latencytop -o /tmp/latencytop.log

Example 4: Specifying the Log Level

The following command sets the log level to all.

% latencytop -l 2

Example 5: Enabling Tracing of Latencies

The following command enables the tracing of latencies caused by
synchronization objects.

% latencytop -f sobj

EXIT STATUS

0

Successful operation.

1

An error occurred.

ATTRIBUTES

USAGE

You must have DTrace privileges to run LatencyTOP.

September 29, 2009 LATENCYTOP(8)