diff -r 578be2adaf3e -r 307f4279f433 Adaptation/GUID-85C18DAF-DB76-51C6-B38D-A802E314F4D1.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Adaptation/GUID-85C18DAF-DB76-51C6-B38D-A802E314F4D1.dita Fri Oct 15 14:32:18 2010 +0100 @@ -0,0 +1,159 @@ + + + + + +Performance +Guarantee Tutorial Describes how to maintain performance guarantees when writing a +software package on a data paged platform. +

Data paging can +affect performance guarantees. When writing software for a data paged platform, +you need to perform an impact assessment on the components of your application. +To do so, you perform the following analyses and implement the appropriate +mitigation for the impacts you discover:

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  • Static analysis,

    • +

  • Use case analysis, and

    • +

  • IPC analysis.

    • +
 + +Perform a static +analysis of the impact of data paging on your code. + + +List all the executables in your package, indicating their size and +pageability. + + +For each item in the list identify its static dependencies, indicating +their size and pageability. + + +For each item in the list identify its dynamic dependencies, indicating +their size and pageability. +For instance, note whether the component is a plug-in to a framework +or is itself a framework. + + +The purpose of collecting this information is to identify which +executables are most likely to be impacted by data paging. + +Perform a use case +analysis of the impact of data paging on your code. It is good practice to +distinguish between use cases involving real time and performance critical +performance guarantees. You do not need to cover use cases which do not involve +guarantees of this kind. + +List all the +use cases for the component which involve real time performance guarantees. +Real time use cases are those having very strict response time guarantees +and also those involving an acceptable user perception of behaviour. +
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  • Video playback,

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  • VoIP phone calls, and

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  • File download over USB.

    • +
 +Examples of use cases involving acceptable user perception are: + +List all the +use cases for the component which involve performance critical guarantees. +This means the bench-marked use cases by which the performance of the operating +system is measure. +Examples of use cases having a strict response time are: +
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  • Standard boot time,

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  • Application start-up +time, and

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  • Camera image capture +time.

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 + +Identify compound +cases involving both real time and performance critical guarantees. +An example of a compound case is receiving a text message while playing +MP3 audio. + + + +Perform an IPC analysis +of the impact of data paging on your code. + +Identify all +performance critical or real time servers which the component interacts with. + +List each case +where these servers read paged data from a client's address space. In this +case, paged data includes: +
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  • Paged heaps and stacks,

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  • RAM-loaded code, and

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  • Read only XIP data structures +including

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    • bitmaps,

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    • constant descriptors,

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    • constant data arrays +in code,

      • +

    • data files accessed +through a pointer, and

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    • exported DLL data.

      • +
    • +
 + +Identify all +cases of custom architectures where one thread reads from another thread's +address space. + + + +Take steps to mitigate +the impacts of data paging which you have identified, as appropriate to each +case. + + +Protect the real +time and performance critical code paths. These paths will have been identified +in the static analysis of the component. There are two ways of protecting +them. +
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  • For all use cases, ensure +that the minimum paging cache size is large enough to accommodate both the +protected code path and any other paged data required at the same time.

    This +method of protection may not always be practical, because compound use cases +may involve unpredictable amounts of data which exceed the size of the paging +cache.

    • +

  • Make the protected code +path unpaged. Mark the code itself as unpaged, and either mark whole regions +of memory as unpaged or pin memory to ensure that it is unpaged.

    • +
 + +Redesign the +component architecture to isolate areas where data paging impacts on performance. +Examples of this are: +
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  • Separating the data +plane and the control plane, and

    • +

  • Splitting a monolithic +library into paged and unpaged parts.

    • +
 + +Use code paging +or XIP ROM paging to mitigate the impact of paging. + +For instance, a monolithic library with static dependences may only +need to be partially loaded, and some dependencies may not need to be loaded +at all. + + +Mitigate the impact of data paging on IPC using the techniques set out +in the document Device +Driver Writing Technology Tutorial + + + + + \ No newline at end of file