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Taskq improvements #455
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Taskq improvements #455
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Under Illumos taskq_wait() returns when there are no more tasks in the queue. This behavior differs from ZoL and FreeBSD where taskq_wait() returns when all the tasks in the queue at the beginning of the taskq_wait() call are complete. New tasks added whilst taskq_wait() is running will be ignored. This difference in semantics makes it possible that new subtle issues could be introduced when porting changes from Illumos. To avoid that possibility the taskq_wait() function is being updated such that it blocks until the queue in empty. The previous behavior remains available through the taskq_wait_outstanding() interface. Note that this function was previously called taskq_wait_all() but has been renamed to avoid confusion. Signed-off-by: Chris Dunlop <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]>
This was referenced Jun 4, 2015
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Setting the TASKQ_DYNAMIC flag will create a taskq with dynamic semantics. Initially only a single worker thread will be created to service tasks dispatched to the queue. As additional threads are needed they will be dynamically spawned up to the max number specified by 'nthreads'. When the threads are no longer needed, because the taskq is empty, they will automatically terminate. Due to the low cost of creating and destroying threads under Linux by default new threads and spawned and terminated aggressively. There are two modules options which can be tuned to adjust this behavior if needed. * spl_taskq_thread_sequential - The number of sequential tasks, without interruption, which needed to be handled by a worker thread before a new worker thread is spawned. Default 1. * spl_taskq_thread_dynamic - Provides the ability to completely disable the use of dynamic taskqs on the system. This is provided for the purposes of debugging and troubleshooting. Default 1 (enabled). This behavior is consistent with the dynamic taskq implemenation found in both illumos and FreeBSD. Signed-off-by: Brian Behlendorf <[email protected]>
Add the TASKQ_DYNAMIC flag to the kmem_cache and system taskqs to reduce the number of idle threads on the system. Additional threads will be created on demand up to the previous maximum thread counts. This should have minimal, if any, impact on performance. This makes the system taskq consistent with illumos which is always created as a dynamic taskq with up to 64 threads. The task limits for the kmem_cache have been increased to avoid any unnessisary throttling and to keep a larger reserve of task_t structures on the free list. Signed-off-by: Brian Behlendorf <[email protected]>
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Jun 10, 2015
Under Illumos taskq_wait() returns when there are no more tasks in the queue. This behavior differs from ZoL and FreeBSD where taskq_wait() returns when all the tasks in the queue at the beginning of the taskq_wait() call are complete. New tasks added whilst taskq_wait() is running will be ignored. This difference in semantics makes it possible that new subtle issues could be introduced when porting changes from Illumos. To avoid that possibility the taskq_wait() function is being updated such that it blocks until the queue in empty. The previous behavior remains available through the taskq_wait_outstanding() interface. Note that this function was previously called taskq_wait_all() but has been renamed to avoid confusion. Signed-off-by: Chris Dunlop <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes openzfs#455
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