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Date: Mon, 29 Oct 2007 23:06:50 +0100
From: Kris Kennaway <kris@FreeBSD.org>
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To: Daniel Eischen <deischen@freebsd.org>
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Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org
Subject: Re: cvs commit: src/lib/libthr/thread thr_mutex.c
 src/lib/libkse/thread thr_mutex.c src/include pthread.h
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Daniel Eischen wrote:
> On Mon, 29 Oct 2007, Kris Kennaway wrote:
> 
>> Daniel Eischen wrote:
>>> On Mon, 29 Oct 2007, Kris Kennaway wrote:
>>>
>>>> Daniel Eischen wrote:
>>>>>
>>>>> The libkse implementation already spins for a bit.  The default
>>>>> number of spins is 500.
>>>>
>>>> OK, cool.
>>>>
>>>>> I'm not sure that another mutex type is warranted, the default
>>>>> mutex implementation should be adaptive I think.
>>>>
>>>> The point being that certain existing applications already know 
>>>> about this mutex name and will use it automatically when it exists.
>>>>
>>>> I am a bit wary of making this the default type though.  The 
>>>> algorithm is a pessimization when the conditions described above are 
>>>> not true.
>>>
>>> I agree, and it applies a little to the KSE approach also.
>>> Spinning is mostly a hack for not being able to tell in
>>> userland if a thread is swapped in/out or is on another
>>> CPU.  If you solve that problem, then you can make the
>>> default mutex adaptive.
>>
>> Yeah.  It looks like Solaris does this.  In principle you could do it 
>> cheaply with a shared page, I'm not sure what Solaris does.
> 
> I think we should add back the thread mailbox for libthr threads.
> I was in favor of keeping the mailbox for libthr, and this might
> be a good use for it.

I am not familiar with that code, can you point me to the change that 
removed it?

Kris