Difference between revisions of "SCHDOPT1 parameter"

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Flags that, in addition to the [[SCHDOPT parameter]], allows one to tune scheduler behavior. <var>SCHDOPT1</var> is a parameter where the following bits control a certain aspects of scheduler behavior:
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Flags that, in addition to the [[SCHDOPT parameter]], allow one to tune scheduler behavior. <var>SCHDOPT1</var> is a parameter where the following bits control certain aspects of scheduler behavior:
  
 
<table>
 
<table>
 
<tr class="head"><th>Setting</th><th>Meaning</th></tr>
 
<tr class="head"><th>Setting</th><th>Meaning</th></tr>
 
<tr><th align="right"><var>X'01'</var></th>
 
<tr><th align="right"><var>X'01'</var></th>
<td>Indicates that threads that are running on a zIIP-capable SRB and need to do journal I/O do not "bounce" to a non-zIIP subtask to do the journal or checkpoint I/O but simply perform it on the maintask. Since generally very little processing is involved in doing journal or checkpoint I/O, sending a thread to an MP task to do the I/O only increases latency and saves no maintask processing overhead.
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<td>Journal and checkpoint I/O cannot be performed on a zIIP subtask; that I/O operation must start on an MP subtask or on the maintask.  When this parameter is set to X’01’, a user running on a zIIP subtask who needs to write to the CCAJRNL/JLOG or CHKPOINT data set, will be switched to the maintask, not an MP subtask, and the I/O operation will start on the maintask.  Waits for an MP subtask to become available on a busy system can be significantly longer than waits for the maintask to become available. There is also more overhead to switch to an MP subtask than to the maintask.  Consequently, this feature reduces wait times to start an I/O to the CCAJRNL/JLOG and CHKPOINT data sets when a unit of work is running on a zIIP subtask.  
  
This setting also prevents a thread running on a non-zIIP task and that has to wait for another thread doing journal or checkpoint I/O before doing the same from bouncing between maintask and subtask to do the I/O &ndash; when the X'01' bit is set, the I/O will be performed on the maintask, again reducing I/O latency. This bit has a much more significant effect if zIIP subtasks are in use. For more information about zIIP processing, refer to the [[SCHDOPT parameter]] and [[AMPSUBZ parameter]] descriptions.
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For more information about zIIP processing, refer to the descriptions for the[[AMPSUBZ parameter]], [[MPDELAYZ parameter]], [[NMPSUBZ parameter]], [[SCHDOFLS parameter]] and [[SCHDOFLZ parameter]].
 
</td></tr>
 
</td></tr>
 
</table>
 
</table>

Latest revision as of 20:57, 15 February 2022

Flags that, in addition to the SCHDOPT parameter, allow one to tune scheduler behavior. SCHDOPT1 is a parameter where the following bits control certain aspects of scheduler behavior:

SettingMeaning
X'01' Journal and checkpoint I/O cannot be performed on a zIIP subtask; that I/O operation must start on an MP subtask or on the maintask. When this parameter is set to X’01’, a user running on a zIIP subtask who needs to write to the CCAJRNL/JLOG or CHKPOINT data set, will be switched to the maintask, not an MP subtask, and the I/O operation will start on the maintask. Waits for an MP subtask to become available on a busy system can be significantly longer than waits for the maintask to become available. There is also more overhead to switch to an MP subtask than to the maintask. Consequently, this feature reduces wait times to start an I/O to the CCAJRNL/JLOG and CHKPOINT data sets when a unit of work is running on a zIIP subtask.

For more information about zIIP processing, refer to the descriptions for theAMPSUBZ parameter, MPDELAYZ parameter, NMPSUBZ parameter, SCHDOFLS parameter and SCHDOFLZ parameter.