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    SubjectRe: [PATCH] Replace timer_bh with tasklet
    On Tue, Jun 18, 2002 at 04:17:45PM -0700, george anzinger wrote:
    > Richard Zidlicky wrote:
    > >
    > > On Tue, Jun 18, 2002 at 11:07:32AM -0700, george anzinger wrote:
    > >
    > > >
    > > > I reasoned that the timers, unlike most other I/O, directly drive the system.
    > > > For example, the time slice is counted down by the timer BH. By pushing the
    > > > timer out to ksoftirqd, running at nice 19, you open the door to a compute
    > > > bound task running over its time slice (admittedly this should be caught on
    > > > the next interrupt).
    > >
    > > I have had some problems with timers delayed up to 0.06s in 2.4 kernels,
    > > could that be this problem?
    > >
    > It could be. Depends on what was going on at the time.

    I have generated high load to test how accurately my genrtc driver will
    work - it turned out that timers added with add_timer occassionally
    get delayed by several jiffies. Results were much worse on IO bound
    load, especially IDE drives, CPU intensive userspace apps didn't appear
    to matter.

    Using schedule_task() to poll the event seems to work without any
    problems.

    > In most cases, however,
    > the next interrupt should cause a call to softirq and thus run the timer list. This
    > would seem to indicate at 20ms delay at most (first call busys softirq thru a 10ms tick
    > followed by recovery at the next tick).

    this was also my impression after looking at the lowlevel interrupt
    handling so I am really puzzled.

    Richard
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