Re: Interesting data on network interrupt - part II

From: Julian Elischer <julian_at_elischer.org>
Date: Wed, 05 Apr 2006 14:40:31 -0700
John Baldwin wrote:

>On Tuesday 04 April 2006 20:33, Paolo Pisati wrote:
>  
>
>>Hi, 
>>
>>i updated my work on interrupt profiling with sone new
>>experiments.
>>
>>In total we have now:
>>
>>-FreeBSD 4 PIC (no asm part)
>>-FreeBSD 7 APIC 
>>-FreeBSD 7 PIC
>>-FreeBSD 7 PREE APIC
>>-FreeBSD 7 APIC JHB
>>
>>Some quick comments:
>>
>>-PIC is much slower in masking interrupt (7k in PIC vs 3k in APIC)
>>-PREE let new thread save less than 500 ticks of 'queue' while 
>> preempted threads are often resumed after a lot
>>-JHB patch shaved 2.5k ticks in interrupt masking op
>>
>>For graphs, data and more comments:
>>
>>http://mercurio.sm.dsi.unimi.it/~pisati/interrupt/
>>    
>>
>
>I'll commit the patch then. :)  One thing you might try to do to better
>measure the effects of preemption is to generate kernel work so that
>the bge interrupts occur while the current thread is in the kernel
>rather than in userland.  In that case preemption should provide much
>lower latency for interrupt handlers, as w/o preemption, an interrupt
>in kernel mode won't run the ithread until either curthread blocks or
>returns to userland.
>  
>

it looks a bit like the preempted threads shuld be put onto a stack of 
threads to resume
so that when the pre-empter finishes, teh previosly active thread is 
resumed.
Basically, a preempted thread should be put at the HEAD of it's run 
queue, and not the tail..
Received on Wed Apr 05 2006 - 19:40:32 UTC

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