Messages in this thread | | | Date | Wed, 06 Jan 2016 13:09:08 -0500 | From | Prarit Bhargava <> | Subject | Re: [PATCH 1/2] kernel, timekeeping, add trylock option to ktime_get_with_offset() |
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On 01/06/2016 12:34 PM, Thomas Gleixner wrote: > On Wed, 6 Jan 2016, John Stultz wrote: >> On Wed, Jan 6, 2016 at 5:00 AM, Prarit Bhargava <prarit@redhat.com> 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. > > We could also extend the fast timekeeper with boot/real/tai extensions and use > that for printk. You can use ktime_get_mono_fast_ns() today. >
Thanks tglx -- I thought about doing that but was put off by the comments in __ktime_get_fast_ns() which point out that we could see backwards time stamps. But I see your point -- I could do the same "last_time_stamp" check and use "??" in the output.
That's a far better approach here, and unless John has any objections I'll go with that.
P.
> Thanks, > > tglx >
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