Performance and Tuning Options

Some of these options increase the risk of DDC/CI communication failures, requiring retries.

Option: --sleep-multiplier

The DDC/CI specification dictates that the host computer wait 40-200 ms (depending on operation) between sending a command to the monitor and reading the response. Typically ddcutil spends approximately 90% of its elapsed time sleeping. Many monitors respond properly with much shorter waits. On the other hand, there are monitors that require longer waits to avoid DDC/CI errors. Option --sleep-multiplier applies a multiplication factor to the DDC/CI specified sleep times. The multiplication factor is a floating point number. For example, 

--sleep-multiplier .5

causes 40 ms waits to become 20 ms, and 

--sleep-multiplier 4

causes 40 ms waits to beome 160 ms.

Note that ddcutil may automatically increase wait times when peforming retries. Option --sleep-multiplier applies to the inital wait time.

Option --sleep-multiplier can significantly speed up ddcutil execution - some monitors have been seen to operate properly with a sleep-multiplier as low as .1,

Option: --async

Enable parallel inspection if 3 or more monitors. See detect command.

Option: --noverify

Skip checking that a monitor has properly processed a DDC Set VCP Feature request packet. For details, see setvcp command.

Option: --maxtries

I2C is an inherently unreliable protocol, requiring retry management.

There are 3 kinds of operations in which retry is possible:

  • Write-only operation. A request packet is written to the monitor with no subsequent read.
    Used only to set a VCP feature value, and to execute command scs (Save Current Settings).
  • Write-read operation. A request packet is written to the monitor, followed by a reading a response packet. Most DDC protocol operations are of this type.
  • Multi-part operation. This is a "meta" operation, consisting of multiple write-read or write-only operations. Used to query monitor capabilities, and for querying and setting Table type VCP features.

By default, the maximum number of tries for each operation type is:

  • write-only operation: 4
  • write-read operation: 10
  • multi-part operation: 8

(Note that the number of retries is 1 less than the number of tries.)

Option --maxtries adjusts the maximum try counts. Its argument consists of 3 comma-separated values. The following example sets the maximum try counts to 3 for write-only operations, 6 for write-read operations, and 9 for multi-part operations.

--maxtries(3,6,9)

A value of "0" or "." leaves the corresponding try count unchanged. The following example changes only the maximum write-read try count:

--maxtries(0,7,.)

The higest value to which a maximum try count can be set, is 15.

Options: --enable-capabilities-cache, --disable-capabilities-cache

capabilities is the most expensive ddcutil command in elapsed time. It is also the most prone to failure on marginal I2C host/monitor connections, due the large number of I2C request/response operations involved.

The capabilities string is constant for any given monitor model. Therefore it makes sense to cache the value.

Capabilities string caching is controlled by options --enable-capabilities-cache and --disable-capabilities-cache. The default is --enable-capabilities-cache. Option --disable-capabilities-cache may be needed for certain edge cases.

The strings are saved in file ddcutil/capabilities within the XDG_CACHE_HOME directory. Normally this is $HOME/.cache/ddcutil/capabilities. This file can safely be erased if the stored capabilities string should become corrupted in some way.

Additional performance related options exist but are experimental. See the Release Notes.