How to call a function in the kernel from Local APIC timer handler

John Baldwin jhb at
Mon Oct 31 12:40:36 PST 2005

On Friday 28 October 2005 07:39 pm, Vaibhave Agarwal wrote:
> Hi, I need some help with the new local APIC functionality added in
> FreeBSD 6.0 and above.
> All the code which I am writing is in FreeBSD kernel.
> I was using LAPIC one shot timer for scheduling some events in the kernel.
> The problem is that I cannot call the function in my code, directly from
> the APIC timer handler, because all the interrupts are disabled in the
> APIC timer handler ( function is lapic_handle_timer() ), and my function
> uses a sleep mutex to protect the kernel code I have written.
> Therefore, I schedule a software interrupt thread, which calls my function
> later in time.
> Is there a way, I can call my function instantly from the
> lapic_handle_timer, bcoz using the software interrupt thread, decreases
> the accuracy of the scheduler i am using.

You can use spin mutexes rather than sleep mutexes in the lapic_handle_timer() 
context.  If you need msleep/wakeup() functionality you can provide that 
using the sleepq(9) interface directly.

John Baldwin <jhb at>  <><
"Power Users Use the Power to Serve"  =

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