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Date: Tue, 09 Nov 2004 10:36:18 -0800
From: Julian Elischer <julian@elischer.org>
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To: Stephan Uphoff <ups@tree.com>
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Subject: Re: cvs commit: src/sys/i386/i386 pmap.c
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Stephan Uphoff wrote:

>On Tue, 2004-11-09 at 13:02, Julian Elischer wrote:
>  
>
>>Can you explain why a spin mutex is more expensive than a sleep mutex (I 
>>assume this is uncontested)?
>>    
>>
>
>cli() and sti() used for the critical section are expensive.
>( The spin mutex includes the critical section)
>
>I recall a USENIX paper about avoiding the cost of cli(),sti() by just
>setting an in memory flag. The interrupt handler was modified to honor
>the flag and delay interrupt processing until the flag was cleared.
>This may have the potential to drastically decrease the cost of a spin
>mutex if interrupts during critical regions are infrequent.
>

yes we USED to do that..
why do we no longer do this?

>
>	Stephan
>  
>