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<a href="https://gitlab.rtems.org/purple-affogato">Ivy Zhuang</a>
commented on a
discussion on <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1358#note_155059">cpukit/include/rtems/rtems/attr.h</a>:
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> */</span></span>
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"><span class="cp" style="color: #999999; font-weight: 600;">#define RTEMS_MULTIPROCESSOR_RESOURCE_SHARING 0x00000100</span></span>
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;">/**</span></span>
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<td class="new_line diff-line-num new" data-linenumber="229" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> * @ingroup RTEMSAPIClassicAttr</span></span>
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<td class="new_line diff-line-num new" data-linenumber="231" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
231
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> * @brief This attribute constant indicates that the Classic API Semaphore</span></span>
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232
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> * created by rtems_semaphore_create() will use the Multiprocessor Priority</span></span>
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<td class="new_line diff-line-num new" data-linenumber="233" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
233
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> * Ceiling Protocol.</span></span>
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234
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> *</span></span>
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> * @par Notes</span></span>
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"><span class="cm" style="color: #999988; font-style: italic;"> * The semaphore instance must be a binary semaphore (#RTEMS_BINARY_SEMAPHORE).</span></span>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">In terms of multiprocessor locking protocols, it doesn't really make sense to use more than one variant per application. From what I've seen, locking protocols tend to assume certain circumstances to do with scheduling, fixed/dynamic task priorities, task allocation, etc. to be ideally increase schedulability, making them incompatible with one another.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">I recall in <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/882" title="SMP: Add FMLP-Short and FMLP-Long locking protocols" class="gfm gfm-merge_request" data-original="!882" data-link="false" data-link-reference="false" data-merge-request="1890" data-project="26" data-project-path="rtems/rtos/rtems" data-iid="882" data-container="body" data-placement="top" data-reference-type="merge_request" style="margin-top: 0px;">!882</a> Karthikey suggests using a locking protocol mask that takes 2-3 bits instead which I think could work well. The attribute set used for <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">rtems_semaphore_create()</code> would probably remain unaffected as well.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">Another option would be to add a configuration option that lets you choose the SMP locking protocol so the protocol information would be stored elsewhere. This would then limit you into choosing to use only one protocol if RTEMS_SMP is defined.</p>
<p dir="auto" style="color: #3a383f; margin: 0px;" align="initial">I'd be interested in hearing what the community thinks is the better option though.</p>
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