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SubjectRe: [PATCH] fix nanosleep() granularity bumps

On Tue, 18 Mar 2003, Andrew Morton wrote:

> george anzinger <george@mvista.com> wrote:
> > Here is a fix for the problem that eliminates the index from the
> > structure.
[...]
> Seems to be a nice change. I think it would be better to get Tim's fix into
> Linus's tree and let your rationalisation bake for a while in -mm.

I'm all for this way. Push my quick'n ugly patch to mainline soon to get
thinks working again. Have at least one mainline release before changing
again to start off from something working. Then add George's patch when
it has matured.

> There is currently a mysterious timer lockup happening on power4 machines.
> I'd like to keep these changes well-separated in time so we can get an
> understanding of what code changes correlate with changed behaviour.

Can this problem be reproduced with INITIAL_JIFFIES=0? Just to make sure I
didn't break something more.


On Tue, 18 Mar 2003, George Anzinger wrote:

> Here is a fix for the problem that eliminates the index from the
> structure. The index ALWAYS depends on the current value of
> base->timer_jiffies in a rather simple way which is I exploit. Either
> patch works, but this seems much simpler...
[...]
> @@ -384,22 +382,26 @@
> * This function cascades all vectors and executes all expired timer
> * vectors.
> */
> +#define INDEX(N) (base->timer_jiffies >> (TVR_BITS + N * TVN_BITS)) &
TVN_MASK

No, with the current implementation we need
#define INDEX(N) (base->timer_jiffies >> (TVR_BITS + N * TVN_BITS) +1) &
TVN_MASK
although I'd like to see that cleaned up.

> +
> static inline void __run_timers(tvec_base_t *base)
> {
> + int index = base->timer_jiffies & TVR_MASK;
> spin_lock_irq(&base->lock);
> + if(jiffies - base->timer_jiffies > 0)
> while ((long)(jiffies - base->timer_jiffies) >= 0) {
> struct list_head *head, *curr;
>

Are the doubled 'if' and 'while' really what you meant?

> @@ -1181,12 +1182,7 @@
> for (j = 0; j < TVR_SIZE; j++)
> INIT_LIST_HEAD(base->tv1.vec + j);
>
> - base->timer_jiffies = INITIAL_JIFFIES;
> - base->tv1.index = INITIAL_JIFFIES & TVR_MASK;
> - base->tv2.index = (INITIAL_JIFFIES >> TVR_BITS) & TVN_MASK;
> - base->tv3.index = (INITIAL_JIFFIES >> (TVR_BITS+TVN_BITS)) &
TVN_MASK;
> - base->tv4.index = (INITIAL_JIFFIES >> (TVR_BITS+2*TVN_BITS)) &
TVN_MASK;
> - base->tv5.index = (INITIAL_JIFFIES >> (TVR_BITS+3*TVN_BITS)) &
TVN_MASK;
> + base->timer_jiffies = jiffies -1;
> }
>
> static int __devinit timer_cpu_notify(struct notifier_block *self,

Why 'jiffies -1'? This will just be made up for in the first
timer interrupt, where timer_jiffies will get incremented twice.


Did you bother to test the patch? It doesn't even boot for me, and I don't
see how it is supposed to.
I'll look into it more closely in the evening. Have to go to work now.

Tim

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