Instruments User Guide: I/O Activity Instrument

Overview


Instrument Description	The I/O Activity instrument captures information about I/O events.
Supported Platforms	iOS
Related Profiling Templates	System Usage Profiling Template

Timeline Pane

The timeline pane displays the following information, based on the instrument’s configuration:


Display name	Definition
Sample Number (#)	The sequence number of the event.
Duration	The duration of the function call in microseconds.
In File (infiledes)	The input file descriptor.
In Bytes (inbytes)	The requested number of bytes to read or write.
Out File (outfiledes)	The output file descriptor.
Out Bytes (outbytes)	The actual number of bytes read or written.
Thread ID (tid)	The thread identifier.
Stack Depth	The number of stack frames in use during this function call.

Record Settings

Click the Record Settings button () in the inspector pane to customize the following recording options.

Sampling Rate

Set how often the instrument records information. The slider allows sampling from 1/10th of a second to 1 second in 1/10 of a second increments. The text field allows for other 1/10th increments. The default value is 1/10th of a second.

System Statistics

Select a statistic to see it graphed in the timeline pane. Click the shape or the color well to change how a statistic is represented.

Select statistics to list

Select the statistics to be displayed in the System Statistics area.

Display Settings

Click the Display Settings button () in the inspector pane to customize the following display settings.

Track Display Settings

These settings control how information is displayed in the timeline pane.


Setting	Description	Options
Style	How information is presented.	Block Graph: Information is presented as a horizontal line until the information changes. The area under the line is filled by the statistic’s designated color.

Active Probes

The following active probes display settings are available.


Setting	Bundled probes	State
File Attributes	`getattrlist` `setattrlist` `listxattr`	On by default.
File Permissions	`chmod` `fchmod` `chown` `fchown` `lchown` `access`	On by default.
Open and Close	`open` `fdopen` `fopen` `freopen` `close` `fclose`	On by default.
Other	`lseek` `fsync` `dup` `dup2` `link` `unlink`	Off by default.
Read and Write	`read` `pread` `readv` `write` `pwrite` `writev`	On by default.
Shared Memory	`shm_open` `shm_unlink`	Off by default.
Sockets	`recv` `recvfrom` `recvmsg` `send` `sendmsg` `sendto`	Off by default.
Stats	`lstat` `lstat64` `stat` `stat64` `fstat` `fstat64`	Off by default.

Call Tree

The following call tree display settings filter the call tree in the detail pane.


Setting	State
Separate by Thread	Off by default.
Invert Call Tree	On by default.
Hide System Libraries	Off by default.
Flatten Recursion	Off by default.

Call Tree Constraints

The following options filter the call tree to display calls that fall within a specific threshold based on the settings below.


Setting	State
# Calls	Off by default.

Data Mining

Allows you to filter through the collected data for specific symbols and libraries.

Detail Pane Columns

Summary Detail Type

The following summary columns are available in the detail pane.


Column name	Definition
#	The sequence number.
Function	The name of the function being called.
Duration µs	The duration of the function call in microseconds.
In File	The input file descriptor.
In Bytes	The requested number of bytes to read or write.
Out File	The output file descriptor.
Out Bytes	The actual number of bytes read or written.
Thread ID	The thread identifier.
Stack Depth	The number of stack frames in use during this function call.
Error	The most recent error during the function call.
Path	The path to the file on which the executable performed the operation.
Parameters	The parameters for the function call. See the API for the specific function for more details.

Call Tree Detail Type

The following call tree columns are available in the detail pane.


Column name	Definition
Self %	The percentage of time the symbol references itself.
Total %	The total percentage of time that the symbol is used.
Library	The name of the library that generated the call.
Category	An icon representing the category of the call.
Symbol Name	The name of the symbol being called.