Date: Fri, 5 Dec 2008 15:09:56 +0000 From: "Ray Kinsella" <raykinsella78@gmail.com> To: freebsd-drivers@freebsd.org Subject: Kernel Thread priority in FreeBSD Message-ID: <584ec6bb0812050709p309d406ax7e22d1fad8ad9719@mail.gmail.com>
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Hi all, I am reposting this from the performance list, as it might be a better forum for the question. I have a problem trying to influence kernel thread scheduling in FreeBSD. There are three threads I am interested the priority of:- a. Enqueue Thread: - Enqueues data in a circular buffer b. Interrupt Handler: - Signals that data in the circular buffer has been processed and in ready for removal - Queues an entry on a task queue so the data is removed from the circular buffer asynchronousily - Data is processed by a pci card c. Task Queue Thread: - Dequeues request from a task queue. - Dequeues data from the circular buffer. *Objective: *I want to prioritise the *Enqueue Thread, *such that it will always executes until the circular buffer is exhausted of space. I want the *Task Queue Thread* to have the lowest priority such that it only runs when the *Enqueue Thread* has no work to do. *Observed behaviour: *I set the *Enqueue Thread, *to have a priority of PRI_MAX_KERN (0) I set the *Task Queue Thread,* to have a priority of PRI_MIN_KERN (64) In the main I see the following scheduling:- ... *Enqueue Thread, *Enqueues serveral requests on the circular buffer *Interrupt Handler*, Interrupts the *Enqueue Thread, *puts requests on a taskqueue for async processing. *Task Queue Thread, *Dequeues the request from a taskqueue and the data from the circular buffer *Enqueue Thread, *Enqueues serveral requests on the circular buffer *Interrupt Handler*, Interrupts the *Enqueue Thread**, *puts requests on a taskqueue for async processing. *Task Queue Thread, *Dequeues the request from a taskqueue and the data from the circular buffer .. No matter what I do with thread priorities, the *Task Queue Thread *always follows the *Interrupt Handler. * *Ideal behaviour* Ideally I would get the following behaviour, were *Enqueue Thread *will always run instead of *Task Queue Thread *thread while it has work to do. *Enqueue Thread, *Enqueues serveral requests on the circular buffer *Interrupt Handler*, Interrupts the *Enqueue Thread, *puts requests on a taskqueue for async processing. *Enqueue Thread, *Enqueues serveral requests on the circular buffer *Interrupt Handler*, Interrupts the *Enqueue Thread**, *puts requests on a taskqueue for async processing. *Enqueue Thread, *Enqueues serveral requests on the circular buffer *Interrupt Handler*, Interrupts the *Enqueue Thread**, *puts requests on a taskqueue for async processing. *Enqueue Thread, *yields timeslices as the circular buffer is maxed out *Task Queue Thread, *Dequeues the request from a taskqueue and the data from the circular buffer *Task Queue Thread, *Dequeues the request from a taskqueue and the data from the circular buffer *Task Queue Thread, *Dequeues the request from a taskqueue and the data from the circular buffer Any idea's how to encourage the scheduler to adopt this behaviour ? Thanks Ray Kinsella * *
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