realtime:technical_preempt_rt
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| - | ====== Technical details of PREEMPT_RT patch ====== | ||
| - | The main aim of the PREEMPT_RT patch is to //minimize the amount of kernel code that is non-preemptible// ((Paul McKenney, A realtime preemption overview [[https://lwn.net/Articles/146861/]])). Therefore different mechanisms are implemented. Those mechanisms are partially available in mainline Linux. | ||
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| - | <WRAP half column> | ||
| - | ===== High resolution timers ===== | ||
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| - | <WRAP center round todo 60%> | ||
| - | This section needs to be edited and filled with a small teaser. The detailed information should be outsourced into an own page. | ||
| - | </WRAP> | ||
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| - | </WRAP> | ||
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| - | ===== Sleeping spinlocks ===== | ||
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| - | In a non-PREEMPT-RT preemption model spinlocks are mapped onto raw spinlocks. A task waiting for a spinlock held by another task spins until the task holding the spinlock releases it. Preemption is disabled in raw spinlock context. In PREEMPT_RT spinlocks are mapped onto sleeping spinlocks, and raw spinlocks retain their behavior. A task waiting for a sleeping spinlock goes to sleep and is woken up when the spinlock is released. In the sleeping spinlock context preemption is not disabled. | ||
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| - | <WRAP rightalign>[[sleeping_spinlocks|Read more about sleeping spinlocks]]</WRAP> | ||
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| - | </WRAP> | ||
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| - | ===== Threaded interrupt handler ===== | ||
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| - | The PREEMPT_RT patch forces the mechanism of threaded interrupt handlers. Due to this all interrupt handlers run in a threaded context except they are marked with the IRQF_NO_THREAD flag. This mechanism can be forced also in Linux mainline kernel without PREEMPT_RT patch by the kernel command line option ''threadirqs''. But there is a small difference in the resulted behavior. | ||
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| - | <WRAP rightalign>[[threadirq|Read more about threaded interrupt handlers]]</WRAP> | ||
| - | </WRAP> | ||
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| - | <WRAP half column> | ||
| - | ===== rt_mutex ===== | ||
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| - | All mutexes in the mainline Linux kernel are replaced by rt_mutexes. A rt_mutex implements priority inheritance to avoid priority inversion. This also applies to sleeping spinlocks and rwlocks. However, the holder of a semaphore can be preempted but does not participate in priority inheritance. | ||
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| - | <WRAP rightalign>[[rt_mutex|Read more about rt_mutex]]</WRAP> | ||
| - | </WRAP> | ||
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| - | <WRAP half column> | ||
| - | ===== RCU ===== | ||
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| - | RCU mechanisms in mainline Linux are only preemptible if CONFIG_PREEMPT is set (Preemption model: "Low-Latency Desktop"). The PREEMPT_RT preemption models both use preemptible RCU mechanisms. Additionally the PREEMPT_RT patch eliminates RCU handling from all intermediate states and processes it only in its own thread. | ||
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| - | <WRAP rightalign>[[rt_mutex|Read more about RCU]]</WRAP> | ||
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| - | </WRAP> | ||
realtime/technical_preempt_rt.1466666891.txt.gz ยท Last modified: 2016/06/23 07:28 by anna-maria
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