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Date: Tue, 6 Jul 2004 16:22:34 -0400 (EDT)
From: Daniel Eischen <eischen@vigrid.com>
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To: Andrew Gallatin <gallatin@cs.duke.edu>
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cc: Julian Elischer <julian@elischer.org>
cc: freebsd-threads@freebsd.org
Subject: Re: pthread switch  (was Odd KSE panic)
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On Tue, 6 Jul 2004, Andrew Gallatin wrote:

> 
> Julian Elischer writes:
>  > 
>  > 
>  > On Tue, 6 Jul 2004, Andrew Gallatin wrote:
>  > 
>  > > 
>  > > FWIW, inserting a pthread_yield() just before the ioctl call in the
>  > > worker thread speeds things up quite a bit (100us -> 73us) in
>  > > combination with kern.threads.virtual_cpu=1.
>  > 
>  > what about with kern.threads.virtual_cpu untouched?
>  > and what about with the hlt sysctl?
> 
> 
> kern.threads.virtual_cpu=2
> machdep.cpu_idle_hlt=1
> 
> no yeild        123.6us
> yeild           116.8us
> 
> kern.threads.virtual_cpu=2
> machdep.cpu_idle_hlt=0
> no yield        111.9
> yield		112.9
> 
> kern.threads.virtual_cpu=1
> machdep.cpu_idle_hlt=1
> no yeild        100.8
> yeild            75.0
> 
> kern.threads.virtual_cpu=1
> machdep.cpu_idle_hlt=0
> no yield         93.9
> ield             67.9
> 
> 
>  > does your worker thread loop to check if there is more work before
>  > waiting to be notified?
> 
> Yes.  He takes a mutex, loops over all completed events, sending
> pthread_signals as required, then releases the mutex and sleeps via
> an ioctl.

Note that he is holding the mutex while calling pthread_cond_signal().
If we enable preemption in pthread_cond_signal(), then I suspect it
would be even worse than without preemption.

I think the only place where it is sane to enable preemption is
on pthread_mutex_unlock().

-- 
Dan Eischen