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Subject: Re: Parallel vs Sequential
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Hi Conor,

You had said that  "<parallel> was not  intended as a performance 
enhancer, but the ant manual says

Parallel tasks have a number of uses in an Ant build file including:

    * Taking advantage of available processing resources to reduce build
      time

Following example was also cited in the ant manual

<parallel>
  <javac ...> <!-- compiler servlet code -->
  <wljspc ...> <!-- precompile JSPs -->
</parallel>

"This example shows two independent tasks being run to achieve better 
resource utilization during the build. In this instance, some servlets 
are being compiled in one thead and a set of JSPs is being precompiled 
in another."

Apart from <cc>, I have also experiment-ed using concat tasks, where 
there will be significant file i/o. Even then <parallel> is not at par 
with sequential. Any clarifications will be highly helpful.

Thank you,

Best rgds
Shreedhar





Conor MacNeill wrote:

>Any performance improvement using <parallel> will depend significantly
>on what you are doing in parallel and on what hardware resources your
>platform provides.
>
>For example, the <cc> tasks could be interacting in ways you don't
>expect.  Maybe these tasks block each other somehow. I have no idea.
>
>In the end, <parallel> was not originally intended as a performance
>enhancer. It was originally designed to allow you to run two operations
>at once, where those operations may block without the other. The classic
>example is starting a server and then running tests against that server.
>These can not be performed sequentially.
>
>If <parallel> can deliver a performance benefit, that would be nice but
>it will depend on your platform.
>
>Conor
>
>
>Shree wrote:
>  
>
>>Hi Stefan,
>>
>>I tried evaluating the performance of "<parallel> task" with sequential
>>way doing(without using <parallel>) a set of tasks. I find <parallel>
>>does not help to improve the performance much and infact it sometimes
>>even slower than sequential(as far I had experimented with some examples).
>>
>>I did several examples. One such method was -  I tried compiling c files
>>in 3 different folders(src1,src2,src3). The destination folder for the
>>created objs were different say src1->obj1, src2->obj2, src3->obj3.  I
>>had 3 xml files, parallel.xml, sequential.xml and template.xml.
>>Template.xml contains the logic for compiling cfiles.
>>
>><!- source of template.xml  -->
>><project name = "template" basedir="." default = "All">
>><!-- the properties are passed as parameters from main build, in this
>>case either parallel.xml or sequential.xml -->
>>   <target name = "All" depends = "create_dir">
>>       <cc name = "msvc" outtype = "executable" objdir = "${objdir}">
>>           <includepath path = "${includes}"/>
>>           <fileset refid = "${SrcID}"/>
>>       </cc>
>>   </target>
>>     <target name = "create_dir">
>>       <mkdir dir = "${objdir}"/>
>>   </target>   </project>
>>
>>Parallel.xml is the main build file that  invokes the target "all" 
>>within a parallel task, so all the c-files in the 3 different folders
>>are compiled into objs parallely while sequential is another build file
>>that invokes the target "all" for each folders sequentially(without
>>parallel task). I expected parallel to finish faster, but found
>>sequential outperforming parallel most of the times.
>>
>>Code snippet from parallel.xml
>>-------------------------------
>>
>><parallel>
>>
>>           <ant antfile="template.xml" inheritrefs="true">
>>               <property name = "SrcID" value="CSource"/>
>>               <property name = "includes"
>>value="${env.include};${basedir}\cSource\Build"/>
>>               <property name = "objdir" value="${basedir}\Build1" />
>>           </ant>
>>                     <ant antfile="template.xml" inheritrefs="true">
>>               <property name = "SrcID" value="CSource2"/>
>>               <property name = "includes"
>>value="${env.include};${basedir}\cSource\Build"/>
>>               <property name = "objdir" value="${basedir}\Build2" />
>>           </ant>
>>                     <ant antfile="template.xml" inheritrefs="true">
>>               <property name = "SrcID" value="CSource1"/>
>>               <property name = "includes"
>>value="${env.include};${basedir}\cSource\Build"/>
>>               <property name = "objdir" value="${basedir}\Build3" />
>>           </ant>
>></parallel>
>>
>>whereas in sequential.xml I do not use <parallel> task. Comparing the
>>time for compiling files in sequential and parallel mode, I find using
>><parallel> does not improve the performance. If one argues that there
>>are " no i/o or legitimate cpu wait/sleep" in the above code,  for which
>>- I also experimented with task that performs file i/o(Concat task) in
>>parallel and sequential mode, still there were no results in favor of
>><parallel> task. What is wrong and where one should use "Parallel" tasks ?
>>
>>Thank you,
>>
>>Best regards
>>Shreedhar
>>
>>
>>
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