On Wed, Jan 6, 2016 at 5:00 AM, Prarit Bhargava <[email protected]> wrote:
> -ktime_t ktime_get_with_offset(enum tk_offsets offs)
> +ktime_t ktime_get_with_offset(enum tk_offsets offs, int trylock)
> {
> struct timekeeper *tk = &tk_core.timekeeper;
> unsigned int seq;
> ktime_t base, *offset = offsets[offs];
> s64 nsecs;
> + unsigned long flags = 0;
> +
> + if (unlikely(!timekeeping_initialized))
> + return ktime_set(0, 0);
>
> WARN_ON(timekeeping_suspended);
>
> + if (trylock && !raw_spin_trylock_irqsave(&timekeeper_lock, flags))
> + return ktime_set(KTIME_MAX, 0);
Wait.. this doesn't make sense. The timekeeper lock is only for reading.
What I was suggesting to you off line is to have something that avoids
spinning on the seqcounter should if a bug occurs and we IPI all the
cpus, that we don't deadlock or block any printk messages.
> +
> do {
> seq = read_seqcount_begin(&tk_core.seq);
> base = ktime_add(tk->tkr_mono.base, *offset);
> @@ -721,6 +730,9 @@ ktime_t ktime_get_with_offset(enum tk_offsets offs)
>
> } while (read_seqcount_retry(&tk_core.seq, seq));
So instead of the do/while() loop above... Something closer to:
int __ktime_get_with_offset(enum tk_offsets offs, ktime_t* base, s64 *nsec)
{
unsigned int seq;
seq = read_seqcount_begin(&tk_core.seq);
*base = ktime_add(tk->tkr_mono.base, *offset);
*nsecs = timekeeping_get_ns(&tk->tkr_mono);
return read_seqcount_retry(&tk_core.seq, seq);
}
Then ktime_get_with_offset() would just call:
...
while(__ktime_get_with_offset(offs, &base, &nsecs))
/*spin*/;
return ktime_add_ns(base,nsecs);
Then you add a simple:
int ktime_try_get_with_offset(enum tk_offsets offs, ktime_t* ret)
{
...
if (__ktime_get_with_offset(offs, &base, &nsecs))
return -EAGAIN;
*ret = ktime_add_ns(base,nsecs);
return 0;
}
thanks
-john
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