Re: No 100 HZ timer !

David Schleef
2001-04-10T12:32:31Z

On Tue, Apr 10, 2001 at 02:04:17PM +0200, Mikulas Patocka wrote:
>
> Adding and removing timers happens much more frequently than PIT tick, so
> comparing these times is pointless.
>
> If you have some device and timer protecting it from lockup on buggy
> hardware, you actually
>
> send request to device
> add timer
>
> receive interrupt and read reply
> remove timer
>
> With the curent timer semantics, the cost of add timer and del timer is
> nearly zero. If you had to reprogram the PIT on each request and reply, it
> would slow things down.
>
> Note that you call mod_timer also on each packet received - and in worst
> case (which may happen), you end up reprogramming the PIT on each packet.

This just indicates that the interface needs to be richer -- i.e.,
such as having a "lazy timer" that means: "wake me up when _at least_
N ns have elapsed, but there's no hurry." If waking you up at N ns
is expensive, then the wakeup is delayed until something else
interesting happens.

This is effectively what we have now anyway. Perhaps the
current add_timer() should be mapped to lazy timers.

dave...