SCHDOFLS parameter: Difference between revisions

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<dd><var class="product">Model 204 V7.7</var>
<dd><var class="product">Model 204 V7.7</var>
</dl>
</dl>
==Description==
==Description==
<p>Applies to z/OS only</p>
<p>
<p>On a z/OS system, <var class="product">Model&nbsp;204</var> zIIP support enables you to offload <var class="product">Model&nbsp;204</var> work from regular processors to zIIP processors.</p>
This parameter applies to z/OS only.</p>
<p>SCHDOFLS specifies the target number of threads on the zIIP offload queue before a non-SRB MP subtask will be dispatched to help the zIIP subtasks and, if started, how aggressively the non-SRB MP subtasks will pick up work from the zIIP offload queue. Setting a higher value of <var>SCHDOFLS</var> will make the non-SRB MP subtasks more reticent to help SRB subtasks out, ensuring better zIIP offload though possibly adversely affecting performance should the zIIPs get overloaded.</p>
<p>
<p>The default value of 2 means that if all zIIP subtasks are active and there are more than <var>SCHDOFLS</var> times <var>AMPSUBZ</var> units of work on the zIIP offload queue, a non-SRB MP subtask will be dispatched as needed and will perform work intended for zIIPs.
On a z/OS system, <var class="product">Model&nbsp;204</var> zIIP support enables you to offload <var class="product">Model&nbsp;204</var> work from regular processors to zIIP processors.</p>
. </p>
<p>
<p>SCHDOFLS has no effect if zIIP SRBs are not in use in an Online (NMPSUBZ=0) or if the number of active SRBs (AMPSUBZ) is set to 0 or if MP subtasks are not allowed to take work from zIIPs ([[SCHDOPT parameter|SCHDOPT]] X'40' is set).</p>
<var>SCHDOFLS</var> specifies both of these: </p>
<p>The [[SCHDOFL parameter]] and [[SCHDOFLZ parameter]] control the scheduling of zIIP/SRB and non-zIIP/non-SRB MP subtasks.   
<ul>
<li>The target number of threads on the zIIP offload queue before a non-SRB MP subtask is dispatched to help the zIIP subtasks. </li>
 
<li>If started, how aggressively non-SRB MP subtasks pick up work from the zIIP offload queue. </li>
</ul>
<p>
Setting a higher value of <var>SCHDOFLS</var> makes the non-SRB MP subtasks more reticent to help SRB subtasks out, ensuring better zIIP offload (though possibly adversely affecting performance should the zIIPs get overloaded).</p>
<p>
The default value, 2, means that if all zIIP subtasks are active and there are more than <code><var>SCHDOFLS</var> * <var>AMPSUBZ</var></code> units of work on the zIIP offload queue, a non-SRB MP subtask is dispatched as needed and performs work intended for zIIPs. </p>
<p>
<var>SCHDOFLS</var> has no effect if any of these is true: </p>
<ul>
<li>zIIP SRBs are not in use in an Online (<var>[[NMPSUBZ parameter|NMPSUBZ]]</var> is 0).</li>
 
<li>The number of active SRBs (<var>[[AMPSUBZ parameter|AMPSUBZ]]</var>) is set to 0.</li>
 
<li>MP subtasks are not allowed to take work from zIIPs (<var>[[SCHDOPT parameter|SCHDOPT]]</var> X'40' is set).</li>
</ul>
<p>
<var>[[SCHDOFL parameter|SCHDOFL]]</var> and <var>[[SCHDOFLZ parameter|SCHDOFLZ]]</var> control the scheduling of zIIP/SRB and non-zIIP/non-SRB MP subtasks. </p>
   
[[Category:System parameters]]
[[Category:System parameters]]
[[Category:Parameters]]
[[Category:Parameters]]

Revision as of 16:11, 28 July 2016

Threshold for task stealing zIIP work

Summary

Default value
2
Parameter type
System
Where set
On User 0's parameter line or reset by system manager.
Related products
All
Introduced
Model 204 V7.7

Description

This parameter applies to z/OS only.

On a z/OS system, Model 204 zIIP support enables you to offload Model 204 work from regular processors to zIIP processors.

SCHDOFLS specifies both of these:

  • The target number of threads on the zIIP offload queue before a non-SRB MP subtask is dispatched to help the zIIP subtasks.
  • If started, how aggressively non-SRB MP subtasks pick up work from the zIIP offload queue.

Setting a higher value of SCHDOFLS makes the non-SRB MP subtasks more reticent to help SRB subtasks out, ensuring better zIIP offload (though possibly adversely affecting performance should the zIIPs get overloaded).

The default value, 2, means that if all zIIP subtasks are active and there are more than SCHDOFLS * AMPSUBZ units of work on the zIIP offload queue, a non-SRB MP subtask is dispatched as needed and performs work intended for zIIPs.

SCHDOFLS has no effect if any of these is true:

  • zIIP SRBs are not in use in an Online (NMPSUBZ is 0).
  • The number of active SRBs (AMPSUBZ) is set to 0.
  • MP subtasks are not allowed to take work from zIIPs (SCHDOPT X'40' is set).

SCHDOFL and SCHDOFLZ control the scheduling of zIIP/SRB and non-zIIP/non-SRB MP subtasks.

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