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From: Jung-uk Kim <jkim@FreeBSD.org>
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Date: Fri, 17 Feb 2012 11:39:21 -0500
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Cc: Alexander Kabaev <kan@freebsd.org>,
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Subject: Re: pthread_cond_timedwait() broken in 9-stable? [possible answer]
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On Thursday 16 February 2012 08:55 pm, Julian Elischer wrote:
> kern.timecounter.tick: 1
> kern.timecounter.choice: TSC-low(1000) i8254(0) HPET(950)
> ACPI-fast(900) dummy(-1000000)
> kern.timecounter.hardware: ACPI-fast
> kern.timecounter.stepwarnings: 0
>
> switching the machine from TSC_low to ACPI-fast  fixes the problem.
>
> in 8.x it used to default to ACPI
> but I used to switch it to "TSC" to get better performance.
>
> I wonder why TSC-low is now bad to use..
> maybe the TSCs are not as well sychronised as they were in 8.x?

Can you please show us verbose dmesg output?

FYI, TSC and TSC-low are not very different.  TSC-low is just lower 
resolution version of TSC for SMP.  Only difference is, we have 
automated your timecounter choice, i.e., if TSCs seem reasonably 
well-synchronized, select it by default but give lower resolution.  
In other words, if your TSC timecounter was never going backwards 
previously, TSC-low timecounter won't, guaranteed.  So, the root 
cause should be somewhere else.

Jung-uk Kim