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SubjectRe: setitimer lowlatency-2.2.13-A1 questions


On Mon, 6 Dec 1999, Ingo Molnar wrote:

>
> On Mon, 6 Dec 1999, William Montgomery wrote:
>
> > I tried using setitimer as a scheduling source for lowlatency testing
> > with generally good results. I left my test running over the weekend
> > and found some large latencies had occurred. It appears that since
> > the signal generation occurs in timer_bh, it is possible for a user
> > task to run between when the timer_interrupt occurs and when timer_bh
> > runs (~2msec in my case).
>
> that should not be possible (except on SMP where there might be a window).
> You are not running SMP, right? The TIMER_BH is run right when the IRQ
> handler returns to non-irq context (which might be user-space or kernel
> space), so it's not possible to 'lose' a TIMER_BH event due to some task
> running. BHs might get delayed due to interrupts though, so you might want
> to profile how long various interrupt sources execute.
>
Oops, forgot to include in previous post -- I am not running SMP.



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