Messages in this thread | | | Date | Mon, 14 Jul 2008 12:03:30 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH, RFC] use hrtimer in sched_clock |
| |
On Mon, 14 Jul 2008, Uwe Kleine-König wrote: > > > I tested the patch on arch-arm/mach-ns9xxx and it seem seams to work. > > > But I admit I didn't test it deeply and I didn't measure if there is any > > > overhead. > > > > There is lots of overhead and your approach is simply wrong. > I expected to have some overhead, but can you please elaborate on > "simply wrong"?
It's wrong because it has a locking problem vs. xtime lock. Try printk() in a code region which has xtime_lock write locked.
> > If you do a grep -r sched_clock arch/arm you'll find a couple of > > examples how to override sched_clock(). > I new that and my purpose was to make this unneeded. Would be nice, > wouldn't it?
It would be nice, but it's simply not possible as each hardware platform has a different hardware which is used for that. Also your approach enforces that the hardware which is used for sched_clock is the same as the one which is used for timekeeping. That's not necessarily a good idea as we can use a less accurate and less reliable hardware for sched_clock() than for timekeeping and we want to do that when the sched_clock() hardware is faster to access.
Thanks,
tglx | |